You could also look at Bass Pro or Cabala’s for a pair of battery powered socks as well. Be cautious though, they are spendy and if he’s diabetic or has circulation issues they may not be the best choice. All my hunting buddies swear by Redhead or the heavy Smartwool socks and they’re out all day in a blind in temps well below 0C. The Redheads have the added advantage of a lifetime warranty as well.
I think this is probably the correct answer. (It is for me.)
So nothing you do in the way of heavier socks, electric heaters, etc. will make any difference – his feet will still FEEL cold to him. The problem is neurological, his feeling in his feet is not working properly. So his feet are at an appropriate temp, but he doesn’t feel that.
The only ‘solution’ is to get him to understand this, so he can stop worrying about it. (And learn the warning signs, so he can monitor his feet – they can’t do that on their own any more.)
Seriously, no knitters here to waffle on about how the only good socks are hand-knitted ones? Because they really are the best, if you can get them. Right now would be a good time for that even if you don’t have any needle-wielding people in your life, because hand-knit accessories seem to be a very popular item on most Christmas markets, at least around here.
When talking hand-knitted socks and natural fibers, best for warmth and keeping your feet dry would be sheep’s wool, although I definitely wouldn’t recommend 100% wool yarns because they’re very hard to take care of especially if they haven’t been chemically treated. Usually they’re handwash only, and very gently so, or you’ll end up with a felted blob of… something. Sheep wool is also not extremely durable on its own, which is why typical sock yarn usually has around 20% - 30% synthetic fiber content to give it a bit more strength.
Merino sheep’s wool is especially soft and toasty, and so are non-sheep protein fibers like yak, alpaca, angora, mohair and the like. But these are all rather flimsy on their own, so not ideal for clothing that’s supposed to see a lot of wear. If anything, maybe a blend of sheep’s wool, synthetics and just enough other protein fiber to give it a bit of a “halo”. A personal favourite would be cashmere because it’s luxuriously soft and warm but doesn’t shed like mohair or angora sometimes will.
Oh, and speaking of other protein fibers, avoid silk blend yarns for winter socks. Silk is better for keeping you cool rather than warm, and in addition to that it doesn’t have a lot of natural elasticity - and that’s not good for people with circulation issues of any kind, unless you can add in some extra stretchiness some other way.