I've found a good base layer that works great. Comfortable, insulated and warm, but still breathable. It's designed to be worn for long periods of a type with plenty of support. It doesn't get too cold in my area (maybe a few days below zero), but even on mild days, having my body covered additional layer does wonder. I'm a fan of underwear. It takes the chill out of any cool day as well. Most definitely, I've found that if my body is cold everything else inevitably is as well (plus I find I catch colds more easily if I don't protect myself).