Neon tetras would be good as the betta is in their first he will be dominant so there will be a very small chance of them nibbling his tail. You could try 2 or more female bettas they look good and he will show of to them and make himself bigger and prettier. That's always good fun to watch. Make sure you get at least 2 otherwise he will always harass that 1 female. That often leads to problems. But when I had my male and 2 females they where fine. Hope this helps.
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