hey all! Thanks for commenting. First off, I named my gorgeous new boy Dusk.
Thanks for all the tips - I've kept bettas before (two males and four females, this is my third male) but it's always nice to be welcomed and get more advice!! :)
I won't be able to get a new tank in the near future, but I heater is a possibility. I will be doing water changes every Sunday and Thursday, with warm dechlorinated water, and I have Dusk in a warm place in the room, away from drafts and windows.
I'll lower the water as well, so he can't escape! ;)