The boring but nonetheless correct answer is wool trousers (I do mean 95-100% wool, some elastane is acceptable I guess though wool has natural stretch anyway) - yeah, they do have to go to the dry-cleaners from time to time but if you hang them up, give them a brush and a hot iron then you can get quite a few wears out of them.
Numerous companies sell them and you can get pretty good clearance deals. A lot of the time it's variations on blue, grey and black but other colours certainly come up. Obviously a pinstripe with a t-shirt is a bit of a statement, but they can definitely be worn casually as long as the ankle is tapered a bit (and you can get that alteration pretty easily if it's not already on point).
I actually have machine washable wool flannels but they're a bit harder to come by. Jaeger tried it a couple of years back.
Wool breathes, insulates when necessary (admittedly there is little real winter weight tailoring off the peg), and performs pretty well in wet conditions. It's what a lot of technical gear is made from.