Military Retro Cargo Pants.
In the military we use to wear these thick heavy cargo pants. They were considered field gear becasue they were considered to be worn on the outside of normal pants. They were kind of baggy and had these side pockets you could put things in. They were made out of some kind of think cotton or canvas like material. I think they could have been more stylish if they were shiny gortex like they make luggage or soft side briefcases with. They kept you warmer but they did breath some since they wee basically a thick cotton weave. Typically cold weather experts tell you to wear clothes in loose fitting layers.
We had to get on the ground a lot and the thing is they could get mud on them but if you let them dry the dirt would just dry up and it could be brushed off. Then you normal gear or pants or long-johns could be kept relatively clean.
Some of these newer Long Johs are made with a type of material that is designed to both pull moisture from the skin and then let it evaporate so they dont get damp. Some people like thermal underpants and some people dont.
You might try looking at some of these hunting or outdoor catalogs or maybe a magazine about hiking. They may make some kind of thick pants for snow-mobilers or something like that for daytime skiers.
Outdoor Gear
Just some examples.
Some dress slacks are made from a heavier worsted wool.