My favorite is actually Gorin-San in Nagano but as you said it's warm now.
For something cozy and off the beaten track, try this in Hokkaido:
KIRORO HOME
KIRORO RESORT-Accommodations
There's a nice pipe there for your snowboard. At least a lot of the info is in English and the locals do know what they are doing. Good luck with the snow though - not a lot of it in the next few days.