Are there any small non-aggressive fish that may be kept in a tank with your Betta?

Yes, there are several small non-aggressive fish species that make suitable tank mates for a Betta, including:

Neon tetras.

Cardinal tetras.

Rummy nose tetras.

Ember tetras.

Green neon tetras.

Glowlight tetras.

Cherry barbs.

Rosy barbs.

Otocinclus catfish.

Corydoras catfish.

Dwarf gouramis.