Cut a piece of 1/2 inch plywood to the size of your mattress, using a circular saw. Slide the plywood between the mattress and box spring to provide more support if the sagging is caused by broken slats or a warped frame in the box spring.
Locate a memory foam mattress pad or cut a piece of memory foam to fit your mattress with a sharp knife. Insert the memory foam between the mattress and box spring. The firm memory foam compensates for the sagging mattress.
Flip your mattress over. Turn the mattress so the original top end is now at your feet. This places the sagging springs on the mattress’ underside instead of directly beneath your body.
Feel the mattress to determine which area is sagging. Lift the mattress and set two to three folded towels under the affected area to provide support to the sagging portion.
Insert an inflatable mattress bladder between the mattress and box spring. The pads provide cushioning support that compensate for the sagging mattress.