I love the concept of a down filled blazer. These blazers are absolutely perfect if you do not real like wearing outerwear in the winter. Put on a sweater, some “warm-ish” pants and your down sportscoat and you are all set. I endorse every down blazer and highly recommend them. Fortunately, they are available at almost every price point.
Uniqlo +J for the lower one, Woolrich for the middle tier and Cucinelli or Moncler Gamme Bleu for the high-end. If you do not have one yet, I highly highly recommend you getting one. Here are two of mine from Moncler Gamme Bleu. I wear these quite often.