The base layer helps regulate your body temperature by moving perspiration away from your skin. You should only use materials such as silk, merino wool or synthetic fabrics (polyester). Some of the bigger names are REI MTS, Patagonia Capilene, Polartec and CoolMax. NO COTTON! Rather than absorbing moisture, these fabrics wick perspiration away from your skin and disperse it on the outer surface of the fabic where it can then evaporate. Thermal baselayers are typically available in light, mid and expedition-weights. Choose the weight that best matches your activity and the outside temperature. Sounds like you might need expedition weight

When I'm skiing I am a big fan of the just classic long john's but as mentioned above REI, North Face and other outdoor brands make good microfleece pants and sweatshirts that are incredibly warm.