Bettas are so fun. My Marshall has a 29 gallon that I upgraded from a 10 gallon, upgraded from a bowl. The reason I kept getting larger tanks was that he really stressed out with the current of his tetra whiper10i filter, which was baffled. The moment I would turn it off(I would run it for 12 hours after checking his water parameters, so he could rest) he would work on a bubble nest and take a nap. The more plants I added the more active he became patrolling his tank.
Eventually the ten gallon leaked and I wanted to keep "gardening" and ran out of real estate to work with. He is more fun to watch in the 29 where he has a veritable jungle to rule over-- he really does make use of every nook and cranny! Lots of caves and tunnels under driftwood. I have a "carpet" of low crypt like plants and he will burrow between those leaves and he gravel and coast along the glass "undercover".
Awesome fish, best $6.00 I ever spent!