I just bought DevonAire PowerFleece Breeches from State Line Tack, and I’m very happy with them! They’re not full-seat, but I do know that DevonAire makes full-seat fleece breeches. I highly recommend them–worn with silk long johns, they are very warm! The ones I got (and the full-seat breeches) are wind-resistant, which is necessary in Nebraska, where 20 mph winds are a light breeze. As warm as those are, though, they won’t cut it for the middle of winter here, which is why I am saving up for Mountain Horse Polar Breeches, which are basically like a ski or snow pant with a full suede seat for riding. Obviously, I can’t speak from personal experience on the quality or functionality, but from what I’ve read, they’re a good breech for when it gets really cold. Typically, I just wear my Carhartt insulated overalls and ride bareback in the middle of winter, but those polar breeches would enable me to ride with a saddle year-round. Hope this helps!