Can a mattress topper firm up a bed thats too soft?

Thank you for reaching out to us about the issues you are experiencing with your mattress. I am sorry to hear that you are sinking too far into it during the night.

It sounds like the comfort layer in your mattress may be too soft. This typically happens when the upholstery layers are too forgiving and lack sufficient support.

The direct answer: toppers soften, they cannot firm up

Unfortunately, a mattress topper will only soften the comfort layers of a mattress. Placing a firm layer on top will not have a noticeable impact, as it will simply conform to the softer layers beneath. To react properly, mattress upholstery must be layered from firmest at the base to softest at the top.

As previously mentioned, our advice is to place a layer of plyboard on top of the base, underneath the mattress. This can help firm up the overall feel to a degree. However, if the mattress has the wrong comfort layers, it is unfortunately not possible to completely change its overall comfort level.

Why a firm topper on a soft mattress does not work

This is one of the most common misconceptions in mattress care, and it is easy to see why. The logic seems sound: if a soft mattress is the problem, add something firm on top.

In practice, however, any topper placed on a soft mattress will simply sink into the softer layers beneath it. The sleeper's weight passes through the topper into the base, meaning the topper does not change the underlying support. It merely adds another layer above the existing ones.

Mattress construction relies on a deliberate structure: the firmest, most supportive layers sit closest to the base, while the softest, most comfortable layers sit at the top. This graduated structure allows a mattress to be both supportive and comfortable. A topper can only add surface comfort or softness—it cannot introduce firmness to the lower layers or change the performance of the core beneath it.

What the plywood fix does and how to do it correctly

Adding a layer of plywood or 3 to 5mm MDF on top of your base—between the base and the mattress—does have a meaningful firming effect by changing the surface the spring unit rests on.

A pocket sprung mattress on a sprung edge divan base feels softer because the base springs provide a second layer of give. Placing the mattress on a platform top or boarding over the springs removes this secondary give, firming up the overall feel. This is the only effective way to make a mattress feel firmer without replacing it.

Please note that this method is most effective for sprung edge divan bases. If your mattress is already on a platform top divan or a solid slatted base, adding boarding will have a very limited effect since there is no underlying spring layer to counter.

The three most likely causes of sinking too far, and the right fix for each

Before deciding on a course of action, it is worth identifying which of the three potential causes applies to your situation, as the solutions differ for each:

1.  Incorrect Spring Tension for Your Bodyweight
Spring tension—the gauge of wire used in the pocket springs—determines how much resistance the springs provide before compressing. Soft tension is calibrated for lighter sleepers (typically under 11 stone), medium suits 11 to 16 stone, and firm is for 16 stone and above. If your mattress was chosen based on showroom feel rather than bodyweight, the spring unit may be too soft. No topper or base adjustment can correct this; the only resolution is a mattress with the correct spring tension. As a slim-build side sleeper, soft spring tensions are surprisingly common in mattresses marketed as medium, particularly in the budget-to-mid-range market.

2.  A Comfort Layer That Is Too Deep or Too Soft
A slim side sleeper (under 9–10 stone) needs a comfort layer that yields to low pressure at the shoulder and hip. However, overly deep or soft upholstery can cause a lightweight sleeper to sink through the comfort layers directly onto the spring unit, losing supportive cushioning. In this case, the issue is too much upholstery of the wrong composition rather than the wrong springs. Adding a topper will not address this, as the problem lies beneath the surface.

3.  Settlement Over Time
If the mattress initially felt fine but has gradually softened in the sleeping zones, the upholstery layers have compressed from repeated use. This is natural and can be managed through regular turning and rotation from day one to distribute wear evenly. If the mattress is single-sided and cannot be turned, this compression will occur more quickly.

When a topper does make sense on a mattress that is too firm

Toppers do have a genuine and valuable role to play, just not in the scenario described.

From my own experience of having a mattress that started it's life too firm for me and my partner, adding a separate mattress topper, softened the mattress enough for it to then be comfortable. If your mattress is slightly too firm for your body weight or sleeping position, a fibre filled topper found on our website here, adds a softer comfort layer at the surface, giving the mattress a more forgiving feel.

Our Microfibre toppers are available in various depths. They provide a responsive, comfort layer that does not trap heat like memory foam toppers.

Adding a mattress topper to a correctly tensioned mattress is a very effective way to tweak the comfort level without changing the mattress itself.

What to do if the mattress is genuinely the wrong mattress for you

We hope that helps and gives you further mattress buying guidance. If you have any more mattress related questions please get back in touch on our contact page or 0161 437 4419.

If after trying the plywood fix the mattress still feels too soft, the most likely explanation is that the spring tension is wrong for your bodyweight, and the honest solution is a replacement mattress with the correct specification. Our guide to soft, medium and firm mattress tensions explains how spring gauge relates to bodyweight and will help you identify the correct specification for your weight and sleeping position. Our how to choose a mattress guide walks through both spring tension and upholstery selection in full.

If you would like to talk through your specific situation and bodyweight before making a decision, please call us on 0161 437 4419. Our office hours are here.

Kind regards, Gary