Along with the previous post. Staying warm can be a matter of nutrition and hydration. It is very easy to get dehydrated at altitude, like in Colorado, so drink enough to urinate every couple of hours. Cotton is made to cool, not warm. I understand there are dry socks, like dry suites available but haven't used them; this was a while ago. I have a dry suit that has a top and bottom, much warmer in ice melt than a wet suit. The abovde comment about a the head is right on the money; If the feet are cold cover the head. This is a mountaining idea and doesn't anticipate standing in water but it helps. At times I have worn wind breaker pants next to skin, poly pro treated w/ silicone spray, and a second wind breaker outside. This was for Sea Kayaking conditions where I anticipated being in cold water for a while.
Regards this helps