I, too, was looking at thermal underwear only for Christmas presents to the unit we are supporting. That was until I found out that the stuff I wanted to send was out of my price range. Tops and bottoms were averaging $62.00 apiece. The reason it was so high was that they were made out of wool. Merino wool to be exact. It's light weight, warm even when wet, not itchy and machine washable without pilling. Unfortunately it's expensive when you need so many pairs.
The Marine Corps news is where the article about banned Under Armour.
http://www.military.com/features/0,15240,93820,00.html
I ended up sending 1 pair of wool socks with a pair of polypropylene sock liners and 1 pair of wool blend (natural products) socks. Polypropylene is not fire retardant but it wicks moisture wonderfully and the pure wool socks will itch on their own. I hope this helps keep their feet warm. Toques were sent for their heads. I was unable to find wool toques or balaclavas. I'm still keeping my eyes open for wool base layers and head gear.
"The only thing necessary for the triumph of evil is for good men to do nothing".
Edmund Burke