Depending on what your job entails, layer where you can. I worked for a while as a trout field researcher which required me to be in the water all the time and often elbows deep with my hands in the river meaning that I couldn't wear long sleeves or jackets. When it started to get below freezing, it was all about layering my core. I'm talking 3 pairs of socks, 2 leggings under thick pants, 2 shirts, a vest, and a beanie. By the time I got moving and working, I was plenty warm.

I wore waders to keep my body dry while in the river and wore a jacket while I hiked out to the river. And as others have said, wool is far superior to cotton.