Mattresses usually are sold with box springs, which are designed to make a mattress firm. However, some people find the support inadequate for their needs and the price undesirable. Fortunately, box springs are not a necessity and you can support your mattress with a sheet of plywood. Plywood consists of several layers of wood that have been glued together. A sheet of plywood that is at least 3/4-inch thick can support a mattress. The low price of plywood may also appeal to those who would rather avoid the additional cost of a box spring.
Take the mattress off the bedspring and take the box spring off the bed frame. Measure the length and width of the box spring. This is the size of plywood you need. A sheet of plywood that is 3/4 of an inch thick may be thick enough to support a mattress, but it is best to consult a sales representative for information about the weight of your specific mattress.
Visit a home improvement store to purchase a sheet of plywood. The store may be able to cut a sheet to your specifications if you cannot find one that matches your measurements. Or, bring home a larger sheet of plywood and cut it to the correct measurements yourself, using a power saw.
Place the cut piece of plywood inside the bed frame. It should rest on the ledge that supported the box spring. Place the mattress on the plywood.