Yeah dimensions would help, Basically what your looking for is smaller Mbuna or maybe some shell dwellers. Brevis are a good start for shell dwellers as they are readily available. For Mbuna you have a ton of options pending dimensions. Some you may have to rehome when they reach there full size but it takes awhile. A good start Labidochromis caeruleus (electric yellows), maybe some afras, demasoni is a good choice as well. Maybe some type of zebras although they can get angry and cross breed as well.
Some you may want to stay away from at first that most LFS have are kenyi (blue females yellow males but man are they nasty.), Johanni or whatever they have labeled electric blues, and any thing out of a mixed tank labeled mbuna. The kenyi and EB are just really aggressive and would make it tough to add the more mild species above. The mixed Mbuna tanks are usually mostly hybrids.
Just some ideas that you will most likely find around you and even at the local chain stores although I would stay away from them if you could.