Flip the mattress over and turn it so the foot is now the head. Many times a sagging mattress is remedied by flipping it to expose the underside. Repeat flipping your mattress every six months to create even wear.
Install a second box spring over the existing unit. This provides the added support of a new box spring while giving your bed extra height.
Place wooden planks or a sheet of plywood between the box spring and mattress. Cut the plywood piece to fit and slip it under the mattress to provide inexpensive support. If using wooden planks, stick with a thickness of at least 1/2 inch and space the planks 6 to 8 inches apart.
Remove your top sheet and cover the mattress with a 1- to 2-inch layer of memory foam. The memory foam provides cushioning support to extend the life of your existing mattress. Slip the memory foam between the mattress and box spring to provide the support without the feel of mattress pad conforming to your body.
Install an air bladder between the mattress and box spring. The bladder is constructed from sturdy plastic and filled with extra air support to keep your mattress viable for longer.