One thing's certain, wet cotton will kill you, or make you wish you were dead.
I have to agree with the other folks about wool pants. I've used WWII "Ike" pants and some German wool pants of unknown origin I got from Cabelas, and they work very well. They would probably be termed medium weight, but are no heavier than denim and very warm. The thrift store dress pants idea sounds like a good one.
I have a Filson double mack and a washable wool coat from Cabelas and like them very much, but they are much too heavy for climbing. My go-to coat is an old Cabelas waterfowl parka, so old that it's made in America. It's a medium weight shell with thinsulate and Gore Tex. It's very light, very warm, and completely wind and waterproof. I can take it off or unzip it for hiking, but even if I don't, it doesn't drown me in my own sweat. Obviously, it's not available any more, but something like it surely is.
I like fleece for it's light weight, price, and comfort, but all of it retains too much moisture for me. The same is true for the ECWACS long underwear I've been wearing lately. I'm looking for a replacement.
