Leftover crib mattresses- what to do with them?

  Now that my boys are both in twin beds their comfy crib mattresses (which we had made by a nearby organic company so they weren't cheap) and I want to re purpose them.  I originally made a reading corner in each of their rooms with the crib mattress, some pillows, and stuffed animals but I'm wondering if there are some other awesome ideas out there?  I would think a friend or cousin could sleepover on the two mattresses pushed together and covered with a thick quilt to mask the split so it seems like a good plan to keep them around, besides I doubt I would get much for them if we sold them.