Mattress Firmness Guide

Mattress firmness is one of the most important factors in choosing the right mattress — and one of the most misunderstood. The right firmness is not simply a matter of personal preference. It depends on your sleeping position, body weight, and whether you share a bed. Choose the wrong firmness and you risk poor sleep, back pain, and pressure discomfort regardless of how good the mattress is.

This guide explains every firmness level, who each suits, and how to choose with confidence.

In this guide:
The Firmness Scale | Firmness by Sleeping Position | Firmness by Body Weight | Advice for Couples | Common Mistakes | Common Questions

The Firmness Scale

Mattress firmness is typically rated on a scale of 1 to 10, where 1 is the softest and 10 is the firmest. Most mattresses available in the UK fall between 3 and 8. Here is what each level means in practice:

Soft (1–3)

A soft mattress allows significant sinkage — your body presses deeply into the surface. Soft mattresses contour closely to your body shape and provide maximum pressure relief at the hips, shoulders, and knees. They suit lighter sleepers and dedicated side sleepers who need cushioning at pressure points.

Feel: Plush, enveloping, cradling.
Best for: Side sleepers, lighter sleepers (under 65kg), those with hip or shoulder pain.

Medium Soft (4)

Medium soft provides noticeable contouring with slightly more support than a soft mattress. It suits side sleepers of average weight who want comfort without feeling like they are sinking too deeply into the mattress.

Feel: Comfortable and cushioning with some pushback.
Best for: Side sleepers of average weight, those who find soft mattresses too enveloping.

Medium (5)

Medium is the most versatile and popular firmness level. It provides a balance of comfort and support — enough contouring to relieve pressure points, enough pushback to keep the spine aligned. Medium suits the widest range of sleepers and is the most common choice for couples with different preferences.

Feel: Balanced — neither noticeably soft nor firm.
Best for: Combination sleepers, couples, back sleepers of average weight, most sleepers of average build.

Medium Firm (6–7)

Medium firm provides more support with less contouring. The surface has a firmer feel underhand but still offers enough give to accommodate the body's natural curves. It is the most commonly recommended firmness for back pain sufferers because it supports the lumbar region without allowing the hips to sink too deeply.

Feel: Supportive with a slight give.
Best for: Back sleepers, heavier sleepers (over 85kg), those with lower back pain, combination sleepers who spend time on their back.

Firm (8–10)

A firm mattress has minimal give. You sleep on top of the mattress rather than in it. Firm mattresses are best for front sleepers, as they prevent the hips from sinking and straining the lower back. They also suit heavier sleepers who need a denser surface for adequate support.

Feel: Solid, flat, minimal contouring.
Best for: Front sleepers, heavier sleepers (over 100kg), those who prefer a very supportive surface.

Firmness by Sleeping Position

Your sleeping position is the single most important factor in choosing the right firmness. Here is a clear breakdown:

Side Sleepers

Side sleeping creates significant pressure at the shoulder and hip — the points where your body makes contact with the mattress. A mattress that is too firm will not cushion these pressure points, leading to discomfort and disrupted sleep. Side sleepers generally need a softer surface that allows the shoulder and hip to sink in slightly, keeping the spine in a straight horizontal line.

Recommended firmness: Soft (3) to Medium (5), depending on body weight.

Back Sleepers

Back sleeping distributes body weight more evenly than side sleeping, reducing pressure point issues. The key concern for back sleepers is lumbar support — the mattress must support the natural inward curve of the lower back without allowing the hips to sink too deeply, which would cause the spine to curve downward.

Recommended firmness: Medium (5) to Medium Firm (7).

Front Sleepers

Front sleeping puts the most strain on the spine of any sleeping position. When the hips sink into a soft mattress, the lower back arches upward, creating tension and potential pain. Front sleepers need a firmer surface that keeps the hips level with the rest of the body.

Recommended firmness: Medium Firm (6) to Firm (8).

Combination Sleepers

If you move between positions during the night, you need a mattress that performs reasonably well in multiple positions. A medium firmness is generally the best compromise, offering enough cushioning for side sleeping and enough support for back sleeping.

Recommended firmness: Medium (5) to Medium Firm (6).

Firmness by Body Weight

Body weight affects how deeply you sink into a mattress. A mattress rated as medium firm may feel soft to a heavier sleeper and firm to a lighter sleeper. Use this as a guide alongside your sleeping position:

• Under 65kg: You will sink less into any mattress. Choose one firmness level softer than your sleeping position suggests. A side sleeper under 65kg may find a medium soft (4) more comfortable than a soft (3).
• 65–85kg: Standard firmness recommendations apply. Use the sleeping position guide above.
• 85–100kg: You will sink more deeply into softer mattresses. Choose one firmness level firmer than your sleeping position suggests. A back sleeper in this range may prefer a firm (7–8) over a medium firm.
• Over 100kg: A firm mattress with a high spring count or dense foam base is recommended for adequate support and durability.

Advice for Couples

Couples often have different sleeping positions, body weights, and firmness preferences. Here are your options:

• Choose medium (5): The most practical compromise for most couples. It suits a wide range of positions and weights without being too soft or too firm for either person.
• Zip and link mattress: Two single mattresses zipped together, each with a different firmness. This is the ideal solution for couples with significantly different preferences or body weights. Each person sleeps on their preferred firmness with no compromise.
• Dual comfort mattress: Some manufacturers offer mattresses with different firmness on each half. Less common than zip and link but worth considering.

Common Mistakes When Choosing Firmness

• Choosing firm because it sounds supportive: Firm does not mean better support for everyone. A firm mattress is wrong for side sleepers regardless of body weight — it will create pressure at the shoulder and hip.
• Choosing soft because it sounds comfortable: A soft mattress that allows the hips to sink too deeply will misalign the spine for back and front sleepers, causing pain over time.
• Ignoring body weight: Two people of different weights will experience the same mattress very differently. Always factor in weight alongside sleeping position.
• Assuming firmness is fixed: Some mattresses have a flippable design with different firmness on each side. Check the product description before assuming you are locked into one feel.

Common Questions

Is a firmer mattress better for back pain?

Not necessarily. The right firmness for back pain depends on your sleeping position. Side sleepers with back pain often benefit from a medium soft mattress that relieves pressure at the hip. Back sleepers with lower back pain typically benefit from a medium firm mattress that supports the lumbar region. A mattress that is too firm for your sleeping position can make back pain worse.

Can a mattress feel different after a few weeks?

Yes. A new mattress — particularly a foam or hybrid — may feel slightly firmer than expected for the first few weeks as the materials settle and conform to your body. Allow at least 4–6 weeks before making a final judgement on firmness.

What does the firmness rating on a product page mean?

Firmness ratings are set by the manufacturer and can vary slightly between brands. A medium firm from one manufacturer may feel slightly different to a medium firm from another. We include detailed descriptions on every product page to help you understand the feel of each mattress. If you are unsure, contact us and we will help you choose.

My partner and I want different firmness levels. What should we do?

A medium firmness is the best starting point for most couples. If you have significantly different preferences or body weights, a zip and link mattress — two singles zipped together with different firmness on each side — is the ideal solution. Contact us to discuss your options.

Ready to find your mattress? Browse our mattress collection or contact us for personalised advice.

You may also find these guides useful: Mattress Buying Guide | Bed Size Guide | All Buying Guides