galactuz,
I would like to correct a bit with what you said. Splenden, imbellis and pugnax consider as wild betta. Although they are surviving in small stream or just a swamp which with rich oxygen. But do provide the air is good. But prefer to have the small or slow air bubble. Hang on back filter or internal filter is the best choice. My pugnax was bred several time in extra air bubble provided.
Unless you are keeping the Half Moon or Crown Tail which bred by the home/farm breeder which they nvr use air bubble.

Beside that, the dried leaves you said... Not all the tree/plant leaf can be used for fishes. Some poisoning dried leaves might kill your fishes. Or some plants was sprayed by some fertilizer or insects killer liquid. Those are poisoning to your fishes too.
The most useful and cheap tree leaf is the Ketapang tree which we called it as Indian Almond tree. Get the totally dried leaf. Wash it and place it inside the tank. You can cut it into smaller piece or dump the whole piece. it is depends on your tank side. And this magic leaf will create the nature black water for your fishes.