I have a attached a image of my setup, as you can see, I have a small hang on filter at the back. But a small internal one will work just as well, a hang on was just my preference. The heater in the other corner. Silk Plants so not to damage delicate fins. The actual tank is about 24 litres and a aqua one tank and it is best to get one with a form of cover, as betta's do jump. You might also find something with a built in filter and light depending what your preferences are. But betta's don't particularly like light anyway, and one thing I find with the all built in tanks is when filter pumps, lights need replacing it is often impossible to find replacement pumps or parts, with my tank I don't really have that issue, I can just buy another filter if need be, lol.