If you have access to your parents still, see if they have a bunch of old comforters.

When family used to visit my house the kids/teens were kicked out of the rooms, which were given to our aunts/uncles. We used to just grab sleeping bags and stack 2-3 thick comforters on top of them. Super comfy, though I'll admit I like a firmer mattress.

I can't stand air mattresses.

You could use something like this as a base: http://www.amazon.com/Coleman-Dunnock-Large-Cold-Weather-Sleeping/dp/B00363PSKK/ref=sr_1_28?s=sporting-goods&ie=UTF8&qid=1411966034&sr=1-28&keywords=sleeping+bag