I just add a layer for every ten degree drop in temperature to the low 20s. Below that, it's just too cold for me, and we only get a couple days a year that cold. Strong headwinds require an additional layer.

All breathable cycling gear for the most part. I have winter MTB shoes, add two pairs of wool socks and finally shoe covers. Regular winter boots on platform pedals for really cold or bad weather. Gloves, glove liners, winter gloves. Balaclava, skull cap, headband to cover ears. Leg warmers, tights, warmer tights, and really warm tights.

Layers, layers and more layers.

I'll also shorten my commute a bit, which is possible because I drive part way. Riding over an hour in really cold weather for some reason is more of a challenge.