The BK Insulator is a must-have. In winter I run a BK more than any other garment. It's the go-to 6 days a week. On the -really- cold days, I even run it as my thermal layer under a Hover jacket, and it works great. It's super buttery soft, compressible and lightweight, with premium goose-down insulation. Two hand pockets, chest pocket, lower hem cinch, and pit zips.
That's all you need.
TR