I am planning to make a winter ascent of a mountain with a height of 4850 meters (15,900 ft). Its summit's lowest and wind-chill temperatures are around -30 C (-22 F) and -40 C (-40 F), respectively. It takes at least 3 days to reach the summit whilst the grade is D and in some parts TD based on the IFAS system.
Right now, I have a pair of winter mountaineering boots which do not have any removable thermal booties. I was wondering how can I use them in this expedition. I have heard from some classic climbers that they used fake wrestling shoes (because the fake ones are cheap) along with wool socks as a removable thermal boot in their boots, in the past. Do you have any better idea(s), that I can apply to my boots regarding this journey?
By the way, I am quite delighted to find this stack exchange website, specifically for outdoor activities with many experts on it :)
It is worth mentioning, my current boots are 2 sizes bigger than my actual shoe size, for example my normal shoe size is 45 based on EUR but my boots are 47. Thus they have extra space for the thickness of additional layer of insulation.
Regarding the usage of wrestling shoes, I have not done it by myself. As they said, they used wrestling shoes covered by wool socks inside their main boots. Therefore, the feet are neither in direct touch with socks, nor the boots. Keep in mind those wrestling shoes which they have used are made of cotton, at least the upper part. But I guess it has some more details which I am not aware of them, plus I do not count it as a rational approach.
Frankly due to uncontrollable variables in the end user, it's quite hard to temperature rate boots and in most cases they are altitude dependent. But based on my boot's brand rating, their extreme temperature are around -25 C(-13 F) to -30 C(-22 F).