The swedish army wool pants are made to be worn with suspenders, just with a normal belt they hang too low and are quite uncomfortable when skiing, running.. Nevertheless I like them very much and exclusively wear the swedish wool pants, they don't get dirty or smelly and I almost never have to wash them. They're also quite strong and durable. Good pockets. As with wool that has fat in it these pants are quite good in drizzle, snow, rain to some extent. I have no problem at all with itching, though I remember I had some years ago when I started wearing this kind of pants, but that was over after some weeks. I think it's definately worth it. I would like such pants that are made to be worn without suspenders though, as suspenders aren't very in at the moment and make it a bit more complicated to go to the toilet. Though it's really warm and comfortable to have the pants covering the lower back. Some people have modified the swedish pants to be good with a normal belt.. my sewing skills are too bad to do the job.
Those filsons look really good, also the east german army wool pants, but I haven't used them. Another positive point with wearing suspenders is ofcourse that you don't need a long sweater or underwear to keep the lower back warm (that's why the jacket that goes with these swedish trousers is short). While with the normal belt trousers you need a longer sweater and underwear to protect the back. At least in the cold weather here in sweden.
The swedish army pants are quite thick and I almost never need to wear a merino longjohns under it, that gets too warm with movement, I'd say you only need longjohns when it's colder then -15C to -20C, keep in mind the windchill ofcourse, and how much movement you plan to do. These pants block the wind quite well.
Tinner woolen pants would be nice for warmer weather, though I'm not sure how strong those would be.
All this said it is difficult to get hold of these pants, even in sweden. That's why I have collected a lifetime supply