If you have a platform bed or a slatted bed frame, you may not need one at all, because the beds themselves will usually give your mattress the support it needs. But if you have an older metal bed ...

Sleeper sofas come in a range of sizes, from loveseats or chairs-and-a-half that convert into twin-sized beds and full-sized ... a tri-folded mattress on a metal pullout frame, a style pioneered ...