Thermal underwear?

Oh Flist! I need some advice. Mom and I have decided to spend a week in Fairbanks in March to try to see the northern lights. We are Californians and thus, are a little anxious about the colder weather up there. I thought, "I'll buy some thermal underwear!" But when I googled it, I discovered a wide price range.

So, for people that buy/use thermal underwear, what is your favorite type? Are there brands that I should totally shun? All help is deeply appreciated.

Actually, while I got you here...how about cleats for the footwear so we don't slip on ice so much? Last thing I want is for Mom (77 years old) to slip and break something while on vacation. Are there ones that are great? Ones that aren't worth a plug nickel?

Again, I will be grateful for any advice.

Thanks!