In reply to Charcot Marie tooth:
Are you already insulating your legs a lot?
An absolute revelation for me was just how much difference it makes having ample insulation on my legs.
My previous thought was that because my legs didn't feel cold, there was little need to insulate them much and so I should just wear a really warm jacket because it was my body that felt cold.
I've since discovered that wearing padded snow-boarding trousers and a substandard jacket keeps my body much warmer than even a top-quality jacket would alone.
I got some cheapo snow-boarding trousers in an Aldi sale (cost £7). My guess is that Decathlon would also have lots of very warm padded trousers and salopettes. It might be worth looking in the fishing section as well as the ski section.
In recent years I've only needed v warm clothes for standing around belaying etc (so that I'm toasty warm before I climb). For that, I have little need for the lightness and freedom of movement that specialist mountaineering/ice-climbing clothes offer (at a price!). I guess (especially for the legs) the same would be true for powered wheelchair use.