Last summer I had the chance to get some Thermals from a company called The Sock Site. I listed it at the left side of the blog under the link named Outdoor Clothing.
I didn't have a chance to try them until this trip. I wore them on Saturday (26 degrees) and I was toasty all day. On Sunday (21 degrees) I purposely didn't wear them and I was much colder. So, I would recommend them if you need some warm "Unders". I got the Duofold model 620A (top) and 620B (bottoms). Not expensive, but warm. They're a blend of 60% Cotton and 40% Polyester. Very comfortable.
I plan on using them when ever it's cold out here, and it's coming.
Till next time, remember: "A bad day fishing is worse if you're not warm".