You have the basics: Helmet, googles, and boots along with the appropriate riding gear. Try adding a chest protector, knee braces or support, kidney belt and elbow and wrist guards. All this gear serves not only as protection but a layer of warmth.

The idea is to dress in warm, breathable, waterproof, and windproof layers. You want to have three layers, a wicking layer next to your skin, a warmer wicking layer in the middle, and your waterproof and windproof layer on top. The first layer, the one closest to your skin, should be a thermal layer made of synthetic materials.