I thought about this idea but I came to the conclusion that it was more natural and versatile to just get regular jeans and put longjohns under them. Also the air layer between the pants and longjohns will also insulate and you can always remove your jeans if they get wet. Cotton as an outerwear is better than when it touches the skin, they even use cotton fibers in the warmest parkas made by Canada Goose. That's my two cents.

Frankie