i think you can get platies and a filter as well
most of the tanks with bettas i have seen have a filter and the filter aint doing any harm to the betta..
i agree with webbie, i think the betta is strong enough to swim away from the filter..
try getting the ones where the motor is not submersible..
i think they have a weaker "pull" compared to the submersible ones..
the submersible motors are usually powerheads, a bit strong :duh:
in my experience though, the only fishes that ive seen sucked by the filter are fish fry, and fish that are weak and dying anyway.. not sure though..