You could get a blue eyed cichlid instead. its convict like in appearence but they are really peaceful, i used to breed them. they are also just as easy to breed, their eyes turn yellow when theyre going to breed and its never failed to indicate.
I also had one with a deformed mouth that was a tiny puckered hole and he survived well into adulthood. pretty cool fish.
infact I even accidentally crossed on with a convict and kept the biggest fry, the pic is several years old but here he is
just an Idea, thought you might be apealed to them.
Or of course for adding fish I would go with Columbian tetras, mine are around 3" long, quite thick and tall and bright blue with red fins.
I would get several cories,
Golden wonder panchax, the males stay small but I had a female that achieved nearly 5" (i think that was a freak accident)
australian rainbow fish, come in many colours, you would want to go either for the smaller blue ones, or the neon dwarfs.
red tail black shark
I've kept all the above fish with a FH I was growing out, as an experiment to see if raising the fh from fry with those fish would make him more peaceful and it did. when I sold him at 6" he was very mellow. so just trying to say that your convict might be fine with all these fish, I've found all the cons Ive had have played great with tankmates.
good luck anyway!
ps would like to add that the FH didn't kill anything at all in that tank, granted it was a 55 so bigger than yours but I'm making a comparison to the FH aggression in a 50gal to a conict in a 29 gal. GOOD LUCK !