Buy a firming pad for your mattress. You have a variety of choices when it comes to mattress pads. Quilted pads, latex pads, convoluted pads and more are available in most sleep shops and some department stores. While a layer of soft foam may make your bed feel softer, a layer of dense foam or a thick quilted mattress pad can make it feel slightly firmer. This may be enough of a difference to improve your sleep.
Consider replacing your box spring to make your mattress feel firmer. The box spring is the foundation for your mattress. The two pieces are meant to work together to provide adequate support and firmness. If your box spring is worn out, broken or otherwise defective, you should replace it with a new one. A broken box spring will not properly absorb the weight of the mattress and the person on it, according to SpineUniverse.com. This lack of support from the foundation will make the mattress feel less firm as a result. A new box spring will likely make a noticeable difference.
Place a piece of plywood between the mattress and the box spring to make your mattress feel firmer. This method is a good temporary solution to a mattress that is too soft. If your box spring is the major source of the problem, then the board may solve the firmness issue entirely until you are able to purchase a new set.
Remember that firmer is not always better for back support. If your mattress is too firm, it will only support the heaviest parts of your body instead of conforming to the entire body, according to SpineUniverise.com. A bed that is too firm is not better than one that is too soft. Either situation will cause your muscles to have to work through the night to maintain proper posture. The idea is for your muscles to get some rest.