Another vote for an Aerobed. We just got a new one (the other lasted 10 years and many many camping trips). We got one of the raised kind which is nice if it's for guests.
DH and I slept on this Air Cloud brand mattress for 6+ months. It held up well, and was comfortable. I've also had Aerobeds in the past - and they were great, too (but, I only have experience with the non-raised aerobeds...)