I have a very weak filter in mine pointed at the glass to break up the current, so that is what I recomend as it doesn't bother the betta, or you can make a sponge filter from some car sponge (A NEW ONE!!!) and some PVC pipe. If you want more info on the sponge filter let me know, its what I have in most tanks now, very good and no current
I think if you did a 10 gallon as follows you should be fine:
1 betta
3 standard corys of choice or 4-6 pygmy corys
Sand substrate
sponge filter
You should be fine. I would recomend that you stay away from the touchy corys like pandas and things, and go for Bronze, Albino or Peppered corys as they do better. Panda corys and a few others need very specific waters, while sterbai and such like much higher temps.