Under Armor Cold Gear thermals, then fleece mid-layer. FYI, if you buy fleece mid-layer pants that are marketed as a hunting mid-layer, you'll pay out the butt for them.......but if you go to Academy and buy some of the cheap, fleece sweatpants, they work just as well and are roughly $10/pair.
I use fleece pajama pants from academy, went one size smaller so they would fit a little snug and not be bunched up under the outer layer. They work very well