get african dwarf frogs i love them so muchhh
guppies also do well for some people, provided you have a bubble stone to oxygenate the water. as do betta, but the bettas cannot live with the frogs.
snails are also awesome and they’ll keep the tank clean!
If you’re willing to invest in a small $50 or so tank filter, you can keep angelfish, a few tetras or guppies, and loaches! Loaches are so fun they look like miniature eels and they eat the food off the bottom of the tank that the other fish don’t touch to keep the tank clean 