Elaine, I don't see why you wouldn't be warm enough walking around with a nice wool layer (tights or long underwear) and whatever pants you want...
What did you wear on the bottom when you were here last January? I don't think you would need anything more than that! You had a lot of layers on. People generally don't wear layers on the bottom, here, unless they are going out to do some serious walking; like when I went to work, I just wore my pants or skirt and whatever tights or socks I would normally wear, since you are not normally outside. Outdoor sports in the cold are another thing, but I have never needed more than mid weight silk long underwear and my Ibex pants, even at -10 F. when skiing or hiking.
Today I had to go to Cambridge for a meeting; it is about 30 but feels like 15. I was cold waiting for the train in just my jeans, but if I had had a nice wool layer under them, it would have been fine. You don't want to be too sweaty!
Robyn