A common feature of the convertible sitting projects is to hide the mechanism that allows couches to become beds, making this function seem more like a defect rather than an advantage.
Adrien Rovero (2010) in Slash overcomes this procedure and shows a minimal sofa bed with just the essential parts: a metal structure that holds a fragmented single pad mattress that gives shape to a chair back seat or to a large double bed.
Sofa bed with a grey varnished steel structure, wooden bed slats, polyurethane foam and polyester padding stuffing, removable cover. Easily converts into a bed big enough for two.