"Get a size smaller to keep taught against skin"
The boot cut thermal next-to-skin layer is quite important to get right while winter mountaineering. It needs to be tight against the skin yet the boot cut prevents boot 'overstuff' around the cuff. I'm quite pleased in how this purchase turned out but I needed to exchange for a size smaller... Smartwool is more... generous than Icebreaker in terms of sizing. FYI.
Smartwool calls these "midweight," but I don't think they make anything heavier. These are the best choice for colder ski days and ice-climbing, because they're nice and warm, but won't bunch up around your boots and socks. The material gets softer and (I think) warmer after you wash them. Very comfortable against your skin and you can wear them for several days without them getting loose or stinky. They dry quickly if you sweat them out. If you have long legs (as I do) they'll cover your knees, but won't fully cover your calves. Not really a problem. These are also very comfortable underneath jeans on cold days. If you don't already insist on merino wool base-layers, you should.