Under Armour Coldgear tops (& leggings).
Very soft, comfortable, and warm.
You can get them in compression or fitted, depending on your preference.
I use them as my base layer (top and bottom) and love them. Switched from regular wool and polyester base layers.
Can't beat under armour. I use the cold gear compression leggings and you can pull them up a bit mid calf if too much is bunched up with your socks. They also have "loose" fit cold gear for a better fitting top. Have both tight and loose. If it's freezing out, I'll wear the compression leggings with the 3.0 base layer leggings over them!