No products in the cart.
How Firm Should a Mattress Be If You Sleep on Your Side?
Mattress firmness for side sleepers deserves a clear, practical explanation. Firmness ratings are the least useful number in mattress shopping. Every brand scales them differently, a “medium” from one company is a “medium-firm” from another, and none of them account for the thing that matters most — how much you weigh and where you carry it.
The short answer. Most side sleepers do best around medium to medium-firm, roughly 5 to 6.5 on the ten-point scale. But that shifts with body weight: under about 60kg you generally want softer, over about 90kg firmer, because the same surface behaves differently under different loads.
Mattress firmness for side sleepers: What side sleeping actually asks of a mattress
Lying on your side, your shoulder and hip are the widest points and your waist is the narrowest. A good mattress lets the shoulder and hip sink in enough that your spine stays roughly straight, while still pushing up under the waist. Too firm and your shoulder is propped up, bending your neck. Too soft and your hips drop, bending the other way.
The simple test: lie on your side in your usual position and have someone photograph you from behind. Your spine should look more or less like it does when you stand. If there is a visible curve either way, the firmness is wrong for you.
Weight changes everything
| Body weight | Usually suits | Why |
|---|---|---|
| Under 60kg | Soft to medium (4–5.5) | Less force to compress the comfort layer |
| 60–90kg | Medium to medium-firm (5–6.5) | Where most ratings are calibrated |
| 90–115kg | Medium-firm to firm (6.5–7.5) | Needs more support under the hip |
| Over 115kg | Firm, with a thick support core (7.5+) | Comfort layers bottom out otherwise |
Where to start looking
Luxe Mattresses covers the medium to medium-firm range side sleepers usually land in, with pressure-relieving comfort layers over a supportive core — the combination that keeps the shoulder sinking without letting the hips follow.
Browse Luxe MattressesAffiliate link — we may earn a commission at no extra cost to you.
Zoned support is worth paying for here
Some mattresses vary firmness along their length — softer at the shoulder, firmer at the hip. For side sleepers this does more good than an extra centimetre of foam, because it addresses the exact geometry problem side sleeping creates. It is the one feature where the marketing and the physics agree.
Things that are not the mattress
- Pillow height. A side sleeper needs a thicker pillow than a back sleeper, because the gap between head and mattress is wider. Get this wrong and no mattress fixes it.
- Knee position. A pillow between the knees stops the top leg pulling the pelvis forward and twisting the lower back.
- The base. A sagging slatted base or a worn divan makes a good mattress feel bad. Check the base before you replace the mattress.
- Age. An eight-year-old mattress has compressed. It is not the firmness rating you bought.
Use the trial period properly
Most online brands give 100 nights or more, and most people decide in the first three. That is too early — your body adapts to a new sleeping surface over two to four weeks, and the mattress itself softens slightly as the foam breaks in. Give it thirty nights before you form a view, and only then use the return if it is genuinely wrong.
If you have persistent pain that a change of mattress does not shift, that is worth raising with a GP or physiotherapist rather than buying a third mattress. Bedding is one input among several.