Because of your tank size another fish is not an option. You could however try a few ghost shrimp or some snails.
While an air pump is unnecessary, you should have a gentle filter and aquarium heater for your betta.
Upgrading to a ten gallon aquarium would give you more options. I keep one of my male bettas in a ten gallon with a school of harlequin rasboras, and four ghost shrimp.
While an air pump is unnecessary, you should have a gentle filter and aquarium heater for your betta.
Upgrading to a ten gallon aquarium would give you more options. I keep one of my male bettas in a ten gallon with a school of harlequin rasboras, and four ghost shrimp.