hello mate there are a few good choices one is bristle nose plecs as they dont get very big and are great algea cleaners but plecs are big poop machines and poo everywhere so i would go with synodontis most synodontis work well in cichlid setups so the choice is yours here is a pic of one of mine mate.
Depends which one you have. Upside-Down Catfish grow to about 4-5". Featherfins get to about 8". Angelicus get to 12". There the most common ones you'll find.