You can get most camo patterns in wool or fleece; it depends upon how much money you're willing to spend. I oftentimes wear 9 oz. cotton and wear my Army ECWS insulated underwear beneath. They're polypropolene with a soft layer of fleece on the inside, and you can find them relatively cheap out of places like The Sportsman's Guide.

I think it's easier to layer, and you're going to come out $$ ahead... I've bowhunted Alabama in December and January, and I never got cold doing this.

Hope that helps.