Some of the ways to increase the firmness of a soft or older mattress are to cover it with a mattress topper or replace the existing box spring with a new one. Another option is to simply flip the mattress.
Adding a mattress topper to a soft mattress allows you to increase the firmness and support you receive. Most toppers are made of foam or latex, and come in a variety of thicknesses. Consider the material used and thickness to determine the pad that matches your specific sleep needs. Memory foam mattress toppers are a popular choice because of the way they conform to the shape of your body and provide more customized support.
Replacing an old box spring with a new one increases the overall firmness you experience while sleeping. The box spring provides added support to the mattress, but over time the wood or springs used weaken and give way. An alternative to completely replacing a box spring is to place a sheet of plywood between the box spring and the mattress. This adds a solid foundation beneath the mattress, making it feel more firm.
Every mattress owner should flip it every six months to avoid creating indentations from the body. If you can’t flip your mattress because it has a pillow top, simply rotate it 180 degrees.