Always on the lookout for clever ways to fit in additional storage, we love this “sofa” made on a base of flat files; their designed to store art and other “flat” works on paper. Look close and you’ll see that a simple (paintable) plywood box has been built to hold the file and provide additional storage on either side. You can buy foam custom-size mattresses covered in cotton slipcovers at Dixie Foam (or make them yourself). We’d have a foam backrest made as well to provide the right amount of support for the pillows, and to allow the sitter to fit on the sofa comfortably without leaning too far back.
Flat files come usually come in colors. You can also buy them second-hand at greatly reduced prices. Many used office furniture companies also provide spray-painting services to transform files with any color you like.