Dude, go with a shell and layers. I too freeze my ass off on the mtn, but was wearing under armour, (sometimes a light weight under my cold gear), then a longsleeve tshirt, hoodie, then a shell, including two pairs of under armour cold gear leggings. After reading some posts on here, I ditched the UA and got a good set of midweight smartwool top and bottoms, then added a mid layer with a shell. SOOOOO much better, lighter, warmer, and gives you more movement. The UA was trapping sweat and making me freeze my ass off in my clothes. Go with a mid weight wool layer and a shell. You'll be suprised how warm you are!