Polarfleece is great but in the winter I lounge around the house in smart wool instead. See http://www.smartwool.com and look at the base layers.
I like it better than polarfleece because it's not as bulky, it's far more breathable (I can sleep in it), and it holds up a lot better in the wash over time. Plus it doesn't get all staticky. It's also warmer! I not only lounge in this, I layer it under running gear to exercise on the coldest days - which is why I initially bought it, but it is just so warm and cozy, I end up lounging and sleeping in it too. It is pricey but worth every penny. It is not scratchy at all either.
I have two sets: a zip top, a crew neck top, and two pairs of leggings. I also have several pairs of socks. I started with the socks (someone gave me a pair for a xmas gift) and fell in love with them. They feel so good on the skin and are so warm! So then I invested in the rest, to replace a polarfleece set that had gotten all pilly and covered in lint. Both my sets are black but you'll see on the web site you can get them in different colors if you want something fun.
If you want something super sleek to layer under jeans and tops and nice clothes, I'd look around for silk long johns - better than thermal because it's thinner. I don't own any silk long johns but I am told they are great.