The H&S stuff seems a bit fragile to me. I never cared for too many of their fabrics, while an English mill their fabrics seem kinda of lux and Italian to me. I really like the roughers Minnis stuff for whatever reason. As for Mohair, like that Tonic fabric, but it is really expensive. I also owned a RTW suit in cotton/mohair and it began to fade really badly. I think it was due to more of the cotton mix in the blend.
How about plain twill, serge, or gabardine? Looks less like jeans and you can still get the texture and weight.
I just thought tan & brown cavalry twill trousers to be "proper classics" for cold weather. I'm not opposed to the options you mention, my only concern with the fabric i mention is the viability of using such a heavy weight for trousers.