I find the Varitherm expedition weight material to be very warm, as well as soft and lightweight.  These are designed to be used by people who need to move, so they are form fitting and moisture wicking.  There is also a 'sportsman' expedition weight model available from Duofold which might be heavier but it is not designed foe moving.  I usually wear 34 pants, and I can even just button 32 size pants, so I ordered the medium (32-34).  This turned out to be a mistake, since the elastic band is very tight.  The material around my legs fit perfectly, but I ended up cutting the elastic with scissors which was a big improvement.  I also ordered the large as a second pair, and these fit my 34 waist without any discomfort, but the legs are just a tad looser than form fitting.  I'm not sure why they use tight elastic at all, especially since they also include a string if you want to make it tighter.