I finally hit on the magic formula: a standard Thermarest, topped by one of their closed-cell foam RidgeRest pads, which easily fit into the Big Agnes sleeve. It's heaven!-=[ Grant ]=-
Kochanski gives the same advice in his Clothing & Sleeping Bags DVD. The closed-cell foam acts like a snowshoe on the softer pads like the open-cell foam. It's funny that people think the rougher you camp, the more you have to sacrifice on the comfort of sleeping while experienced survival instructors teach that to work on the comfort of your bed is a top priority so as to help conserve energy and think clearly in the roughest camping level there is, having to unexpectedly survive in the bush totally cut out from civilization.
Frankie