Place a 3/8-inch plywood board on the box spring, and set the mattress on top of the board to create a firm resting place. You need an electric saw, measuring tape, a marker, sandpaper and the mattress.
- Measure the mattress
Measure the length and width of the mattress. Use these measurements when purchasing a large plywood board. Depending on the mattress size, you may have to purchase two plywood boards and place them beside each other on the box spring.
- Cut the plywood
Place the plywood on the box spring. If it requires cutting, set the plywood on the floor, and place the mattress on top of it. Use the marker to trace the mattress curves onto the board. Take the plywood outside, and use an electric saw to cut the plywood into shape. Use sandpaper to smooth the edges.
- Place the plywood on the box spring
Bring the plywood inside, and set it on the box spring. Place the mattress on top of the plywood, and cover the mattress with bedding.
- Test the firmness
Lie on the bed to test its firmness. Roll from one side to the other to check for dips. If the bed is not firm enough, add another plywood layer.