You could try some fantail guppies - I found that they were really
hardy - one time I forgot to put dechlorinator in my new water - all
the neons died but the guppies swam around merrily as if nothing was
wrong!

Anyway, guppies will swim all over the tank, but they are kind of dumb,
they don't really have any personality as far as I can tell, they just
follow your finger and beg you for food.

Maybe you could get some neons or some kind of schooling fish - neons
are pretty, and swim a lot as well. They can be a bit touchy though,
and you'll need a heater. They say guppies need a heater as well, but
I've kept them successfully without one, depends on your climate I
suppose.