RECOMMENDED GEAR-MID LAYER
Polar Fleece or wool Sweater
A good sweater is worth it's weight in gold. Thick wool is optimal but expensive and somewhat hard to find. Polar Fleece makes a good second choice, it will stink quicker and isn't fire resistant like wool, but it isn't itchy.
Poly Pro Thermal Bottoms
I lived in a pair of these for 50 days and they really should be washed every week, let me tell ya they collect an odor. The bright side is they are about the warmest thermal bottoms you can find. Get a larger size and wear them over your regular thermals. Poly pro's should not be worn directly on skin or at all if large amounts of physical activity are projected. The materiel can actually wick too much moisture from your body and cause your body to burn calories to compensate.