Ditto, I am also interested on any input from others who have dabbled in the field that OP mentions. Being from the Northeastern United States, I have always just picked up base layers of various thickness from L.L. Bean, like this: https://global.llbean.com/shop/Long-Underwear-Base-Layers/51...

I don't think of this as a technology or expensive, though. They are somewhat pricey, but can be worn for many winters and thus have good value.