I am not sure we are the correct forum to address this issue. I would look around on the internet about what gear they use at McMurdo Station, in Antarctica. I have been winter mountaineering in -40, but not in the day- that was our night temperatures. We would ski into a base camp and then make a huge snow cave to live in for a week and attempt climbs from the snow cave. But this was in the early 1970's and I am sure there is different/better equipment out there now so I hesitate to suggest what I used. I also used the white Micky Mouse boots and they kept my feet warm when in camp. While skiing, we just used regular leather x-c ski boots (with lots of wool socks and the boots had huge boxy toes) since we were actively moving and it would warm up to about 0-degreesF.

The actual location and intended activities would also make a difference in the clothing. What is this person going to be doing?