I think pygmy rasboras may be betta snacks. I had them & they're tiny! Definately betta mouth size but it can depend on your betta's "personality". CPDs (celestial pearl danios or whatever they're called now) might be ok, mine were very shy even with other small fish like rosy loaches...there's a thought...not sure it's a good 1, my rosies were shy too (with CPDs).
Hmm, a 10g is so small, maybe espei or hengle's rasboras? I'm not sure if you mean just Asian fish or more specifically where bettas a native...I bet they don't have too many rice paddy mates in little puddles, lol.