Well, you will never have the trim polo n breech summer look in winter! But I think you can look bundled up in clean, well fitting, athletic or outdoor gear in colors that suit you and the horse.
PNW here where we do go below freezing but mostly contend with cold rain.
I ride outside most of the time and have a huge supply of low volume layers. From October to April it’s some combination of base layer long underwear top n bottom, cotton thermal, microfiber, merino wool, or microfleece. Then on top lightweight wool pullover, hoody that’s fleece inside, slick outside, then down vest, parka, long rider rain coat, waterproof jacket as needed. Regular breeches over the long underwear or kerrits fleece winter breech. Heavy wool socks and Ariat insulated waterproof paddock boots and half chaps if needed. No scarf. Fleece gloves with gripper palms.
I think outdoor and sports gear translates better to riding than regular clothes. Though it is nice to find a purpose made riding parka as most ski or snowboard jackets bunch up around the middle when you try to ride in them.
Color is also important, seriously 
it can be hard to look tidy if you are bundled up in clashing brights or pastels. Choose a color family that suits you and your horse and darker breeches not beige can look more pulled together with winter gear.
If you are riding and teaching you might want a knee length down parka (North Face or North Face knockoff ) to stand around in.
The plus side of winter clothes is that they hide muffin tops, panty lines, and all the other wobbles that are on display all summer!
