We've bought our mattresses online from the Foam Factory. Five inches of foam and two inches of MF. The MF is stiff when it's cold but we preheat with a 12V electric blanket for a half hour on those nights. If I was planning on camping in November here in the Rockies, I'd forgo the MF, but it's doable down into the 30ºs.
A queen sized mattress fits in our 58.75" interior just fine. They'll do a custom size, but it's quite a bit more expensive.
I built our five-wide in 2013 and the initial trip was to Zion. When we were almost home my better-half says, "It's not that big of a deal coming home anymore." I'm thinking something is wrong. We'd had a great trip so I ask her, "what are you talking about?" And she replies, "the mattress in the teardrop is as good as our bed."
I think it should be a felony to build a teardrop and cut corners on the mattress.
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