We've just got a double sofa bed that really needs another foam mattress to go on top to make more comfy and raise the height for MIL. Lots of foam ones available but they all say you can't roll them up to store away once they've been unrolled for the first time. Ikea do great ones (we've got a couple that we've used for kids sleepovers for years) but they only come in single size. Does anyone know of a decent thickness double foam mattress that can be rolled-up?