To be honest new world cichlids are the wrong type of fish to go with for a multi-cichlid display. Although it's the most common method among amateurs I don't think people realize that keeping them this way pretty much keeps their natural behavior (the character that makes these cichlids cichlids) at bay and the fish end up surviving but not thriving. Unless you want to upgrade tanks, I'm not willing to recommend anything for your convict. (If you post in the new worlds section I'm sure people will give you ideas to try, but whatever you do, don't go mixing Africans with the convict).
On the other hand if you got rid of the Convict and started over with an African tank you can do a nice little community. Cichlids from Malawi, unlike new worlds like convicts, thrive in crowded environments, and their colors are very intense to boot. A 25 gallon isn't much to work with, but you can manage something. If you're interested in taking this route say the word and we'll get some ideas going.