A sleeper-sofa mattress upgrade: Milliard 4.5-inch Memory Foam Replacement Mattress It doesn’t take much to improve upon the busted, old mattress—or the disappointing new one—lurking in your sofa bed.

Potentially the hardest working piece of furniture out there, the sleeper sofas of today are far and away better than the ones of yore — you know, like that pull-out couch in your childhood home’s ...