I would own a sofa bed if I could find one like this: http://www.campaignfurniture.com/archivesdetailspage.asp?stockNo=80921&imgNo=2&archive=1
I’ve figured out the folding seat cushion (tri-fold mattresses made from 4" laminated foam) and the folding mechanism. The hard part is the legs and the fittings, which are not actually that difficult, just rare now. If this could be built in 1805 for use during war, there’s no reason we can’t be making the same thing now.
