Nice fish! As said, if at all possible, try and bump the tank size up. Not only really for space, but it truly makes your job much easier as far as water changes and stuff goes.
I dont recommend putting any sort of shrimp or snails into the tanks you currently have. In fact, dont add anything in unless its 5 gallons or larger, since ammonia cranks up super fast in something smaller with that many inhabitants.
Aim to get 2+ gallons of a tank. Many vases are this size, too, and at a good price. Look for ones without narrow necks. Bettas enjoy more horizontal space and surface area.
I know you said your temp ranges from an acceptable 24-28'C (75-82'F), but it is important that the fish's temp stays stable. Try and keep the temps as stable as possible within that range, and consider getting some of those cheap, suction cup tank thermometers to help!
I hope you try the live plants! Theyre fun and help keep your tank a bit healthier and many types can help keep ammonia down-- great for you because its means a bit (bit!) less work, and for the fish, it means a safer tank.
I have a thread about easy to care for plants, most will do very well in a smaller size tank.
Good luck, and welcome.