Very light, breathable windbreaker (wind shirt) either over, or under, my wool outer layer.
Windshirt under your outer layer works quite well.
For significant rain,snow, sleet, etc… then I'd go with a quality shell as the outer.
Shot outside here in northern Vermont all through last winter; most I ever wore was my Austrian wool surplus sweater, with appropriate layers underneath.. and my featherweight 1/2 zip wind shirt (breathable, not waterproof) under it. Cant fit it over! But do wear it over my next best wool sweater sometimes.
Worked for me down to 0F or below, and I get cold easily.