For many the guest bed has for years been the sofabed. But they are usually terrible beds, with too-thin mattresses that get lumpy. People are moving more towards inflatable beds they put on the floor or a stand. On the floor of course is not comfortable either.
So why not a sofabed with an air mattress inside, a quality one like those found in the higher-end airbeds. Those are quite nice to sleep on, with adjustable firmness. You can't have the thick foam walls, those would have to be inflated, but you could have the foam padding on top. Could auto-inflate with built in pump.
Would be a good idea in RV sofas as well.