I'm allergic to wool, and used to sweat in the poly blends, but silk works well if it is not super cold. Also cool-max works well for me. Either one is thin and not bulky, and I wear fleece breeches over the top with tall Stateline tack riding boots. Up top is a turtleneck with a sweatshirt and sweatjacket over that. I usually have to start peeling off a top layer once I get moving well.
However, I am in the south, so I only need the thermal layers on the really cold days, when it is 15-30 degrees
The problem I have is keeping my fingers from freezing and still be able to hold onto the reins...any ideas??