If you can't afford some of those great Viking undies that I have on sale (demos starting at $75) you might want to take a visit to
The Sportsman's Guide, a great sporting goods / outdoors store that has a good internet outlet.
Go the the ''Men's Clothing -> Underwear'' section.
There are a few great selections there, particularly their own in-house version (Guide Gear) of the US Army's ECWCS 10 oz. Poly - Fleece underwear.
When buying tops, always get the TALL version so the tails are longer. The Union Suit bottom is nothing less than incredible.
Go with a thin layer of non-fleece polypro (or even silk!) for a wicking layer under the 10 oz.
After that you can throw on a wool sweater, or even a 60/40 nylon/cotton jogging suit, about the
only time you can get away with a cotton blend.
High % of cotton blends can be used in warm water to help keep you
COOL, so stay away from high cotton content if you wanna be warm.
No, I don't own any stock in the outfit, I've just been buying from them for over 10 years & have spent 4 hour stretches in 28° water & come out comfy.