How to Make a Bed Firmer in the Middle

Remove the mattress and box spring from the bed.

Inspect the bed frame to make sure it is assembled correctly and that all the screws are tight. If you have a queen or king sized bed, the bed frame should have support legs going down the middle. If there are no problems with the bed frame, proceed to the next step.

Inspect the box spring. Lie down on the box spring while it rests on the floor. The box spring should feel firm underneath you.

Place the box spring back onto the frame.

Lay a 3/8-inch-thick plywood piece on top of the box spring. Ensure that the plywood is same size as the box spring -- no more than 1 inch smaller. Don't let the corners of the plywood stick out. Use one piece of plywood on full beds or smaller and two pieces for queen size beds or larger. If you use two pieces of plywood to cover the box spring, situate them horizontally so the two pieces don't run from the top to the bottom of the bed. This will provide better support.

Place the mattress back on the bed and make the bed. If you find that this does not make your mattress feel firmer in the middle, you may need to replace the mattress and/or box spring.