I should also add, if you can find one, try a gentle submersible filter for the tank instead of a hang on the back. Many Betta -really- don't like the flow of HOB's. I currently have a Duetto DJ50, which is the filter I'd make if I were designing a Betta filter. Sadly, the Duetto is getting really hard to find and I think they stopped making them.
There are other options though, like the fluval submersibles. I have not used those but will likely have no choice in the future if I keep desiring more Betta tanks LOL.
Also avoid air "bubblers", some Betta absolutely freak out with them.
2 10 gallon tanks, 1 20 gallon tank, 1 Fluval Edge, 1 29 gallon tank, and one backyard pond.