very small coldwater tank

Are there any coldwater aquarium species that are suitable for a tiny
aquarium (3 gal)? I know it's a real challenge to keep anything smaller
than 5 gal but I've very little space, and moreoever a few species can
live happily enough in tiny quarters (eg Bettas) if you keep it clean
(and I won't mind changing the water etc. every other day, for
example--it's no great chore with a tiny aquarium). Unfortunately
bettas are NOT coldwater tolerant at all, otherwise they'd be the
obvious choice.
So what small species can survive at about 10*C (lowest temp of my
centrally heated room in winter)? White clouds seem ok, but there
wouldn't be quite enough space for many in 3 gal, and I don't think
they do so well when not in schools. Paradise fish take lower temp ok,
but if I'm correct unlike Bettas they grow a bit big for 3 gal. Guppies
might be fine, although they're not my favourites. Bronze cories
apparently can live at low temps (and even breathe a bit of air), but
not sure if I'd also need to keep them in a school.
I'm insisting on coldwater as arranging heating for a 3 gal tank is at
best fiddly. I think what I need is suggestions for subtropical
species, small ones that don't need a ton of oxygen (if I can get away
with aeration I'll do that too, although I know it's not likely).
Please share your thoughts,

Seb