[Sugarfoot]

Unfortunately, Airstream did and still does design with somewhat of a "custom" size mattress. Mine in the Tradewind are the same 34x75ish size as yours. Actually, we can be thankful that our mattresses at least have corners with right angles, not with rounded like some models.

There are places that will custom make a mattress to a specified size. Another option is to have foam cut to size, upholster or slipcover it. That's what the previous owners did. We added a 3 inch memory foam topper to each. A king size 3" Serta memory foam topper from Overstock.com yielded enough for each twin and a dog bed to boot. The stuff cuts pretty cleanly with a straight edge razor blade or box cutter.