If you are going to keep fish in a smaller tank or even a bowl I would recommend keeping small fish that consume very little food and therefore produce very little waste.
We have several tanks of Endlers that have no filters but only an air stone which can be powered by a nearly silent USB air pump. Because we heat the room we do not need to use heaters in our aquariums unless we have to deal with an illness.
The reason we don't need any filters is because our whole aquarium acts as a filter. The tanks have a good amount of substrate in them with lots of plants and the tanks have been set up for many years so there is plenty of beneficial bacteria on the surface of everything in the tanks.