I'll be in the espace Killy at the start of Feb. About 80% of the people there are British, so the main holidays to avoid are the British ones - half term is over two weeks, 9th-23rd Feb and Easter is (guess what?) over Easter. Anyway, you'll find it very hard to get accommodation then.
w/c 16th December they sold 5000 lift passes (typical for a low season week). Over xmas they expected to sell over 18,000. You'll like it better uncrowded!
Snow hasn't been great yet this year but most of the lifts are openwww.valdisere.com
are both helpful with trail maps etc).
If you want to stay somewhere cheaper but with no nightlife then Tignes or Val Claret are much cheaper. The whole ski area is well-connected (in fact I think the skiing is best starting at Val Claret as the worst part of the area is the runs back down to Val d'Isere which get very rocky and icy).