You need someone more creative than I to chime in here.....
In homes, people use pillows, but that leaves you with a lot of pillows to store. Same with a large rectangular piece of foam wrapped in cloth.
I wonder if an inflatable twin mattress would work, but you'd have to store that too. Inflatable pillows would probably be the lightest and easiest to store.
You don't want to make them too comfortable or they'll never go home.