I've got whatever they call the EMS equivalent of Smartwool. A couple of companies produce what is basically the same sock, but they call them slightly different things.
One thing to remember when wearing warm socks, especially multiple pairs: Don't tighten your shoes up too much over the bulkier socks. This squeezes the air out, and it's a layer of warm air that keeps your feet warm. So loosen your shoes a little more than usual so that they feel similar to how you tie them over thinner socks.
Thicker socks keep your feet warmer because they trap more warm air close to your skin than thin socks do. Don't squeeze all the air out of them or your feet will freeze.