the snail that poops the least is a nerite. I would really consider it first.... I have two in a 20 gallon and it is a giant mess!! And I wanted to thank you for being responsible. Most people don't have a clue about bettas when they buy one, but you actually did some research (or had prior knowledge?) and you are awesome for that. It's so nice to welcome someone like you to the forum!! And like someone said before, a lot of times people here will sell plants or little plant starter packs that can really help you get started. Then you can have a variety and see what works, what doesn't, your preferences etc.