Betta’s have different personalities, so what works for one betta won’t work for another.
My parents have a betta named Ralph in their home in Ohio. Ralph lives with a snail named Clarence. Ralph is a very passive fish and just likes to lay on the bottom or occasionally swim near the surface. His tank is fairly large (1 gallon) but he could live in a smaller one and be perfectly fine.
Right now I have a betta named Destroyer who thinks he’s Chluthu’s gift to the world. He’ll investigate anything he sees in the tank and is not afraid of my fingers. If we put him in a smaller bowl/glass to change his water, he gets very angry and will butt the sides of the glass with his head. Right now he lives in one of those betta starter bowls with two plants to nap in. It’s .5 gallons, but if I got him a 1 gallon, I’m sure he’d love it. We also got a snail named Crouton to clean his tank, but he started trying to eat Crouton by the second day, so we had to remove him. I’m sure if we added any of those other fishes that get along with most other betta, he’d try to eat them too. If we show him a mirror he goes insane.
If you want to see two bettas fight without harming them, then you can get one of those duel bowls. They won’t look at each other all the time, especially if you get additional plants to put between them, but if you shine a fight down the middle and direct them towards each other, you should see some action.