The night I spent on an air mattress ranks high in the Bad Sleep Hall of Fame. It felt like sleeping on a giant egg carton, so I let some air out. Then it was too soft. My shoulder hit the floor when I lay on my side, and if either my sleeping companion or I so much as twitched, the whole tormentatious bed would undulate for a minute or two. Don’t put your guests in this situation. Unless you wish them to go and ne’er return.
I can suggest a few alternatives to the evil, uncomfortable, cheap air mattress. It’s possible to buy a good, comfortable air mattress made of rubber or latex. These not only avoid PVC but are also sturdier and more durable than their vinyl cousins. Or so I’ve read. Trouble is, you can’t figure out which ones are actually comfortable without testing them out; you’ll have to look around for reviews on the web, or just guess and be ready to ship it back if necessary.
A plain old piece of solid foam or latex might also work. In fact, I currently have a single foam mattress kicking around that I use for this purpose. It’s incredibly lightweight. Your local foam store or an online supplier will happily sell you a large piece of firm foam — unfortunately it is likely to be impregnated with fire retardant and health retardant polybrominated diphenyl ethers (like mine, which is a hand-me-down).
IKEA, which is PBDE-free, sells foam and latex mattresses; some of the foam ones could be rolled up and left in the closet, and they aren’t too expensive. If you don’t have access to IKEA, look about on the web for latex mattresses. A latex (or foam) pad might be too hard and/or thin for some guests, so you could store a feather bed for use atop.