I usually wear a H/H base layer and a soft shell, but my jacket is just a shell. This way I can just have one jacket for winter and spring, and it's easier to adjust to different temperatures. And the H/H base layers aren't skin tight, but they're fairly snug on me. I guess they're not restirctive at all, but not loose so they don't get in the way--kind of hard to explain unless you see it. But yeah, lots thin(ish) layers is the way to go for sure.
if you want something thin and breathable go and get yourself some cheap microfleece at walmart or target. just get a thin microfleece or polyester long sleeve shirt. put a t-shirt or hoodie on that and your good.
i generally just wear a hoodie under my jacket, so t-shirt + hoodie + jacket when it's colled. i also usually wear shorts under my snowpants, i guess it's been pretty warm the last few times i skiied so it hasn't been too much of an issue. but i'm living out east now so i might have to invest in some other layers. underarmour should work good, i have some i bought at the end of last season but i never wore it, i think it's pretty expensive though
The bottoms are kinda tight, especially around the ankles. Its kinda a good thing tho because it seems to stop that nasty habit of your underlayer folding up in your boot and being a pain in the ass. The tops they make are also really really really good. I highly reccommend mine that I bought last month, its loose, light and keeps heat in like a motherfucker when you have a layer over it. I've used it for running, and it so nice. So nice. If its cold, I put a t-shirt over it and it keeps me really really warm, but even in august I could run with it, as alone, it wicks moisture away so fast that it cools you, and keeps even me, a honestly pretty sweaty guy, dry. Amazing stuff, well worth the $40 I paid in the store for it. It shows up around here every so often, snag some when you see it.
And also, I'm sad that other ski companies that make outerwear and softgoods normally dont ever reach into this market. It would be cool to have some more choice and style when it came to it (HH has taken it a step by doing something cool with their sleeves, but more is needed!)