If you really want to keep an ca/sa tank, how about staying with a couple female convicts, a couple female firemouth, A small-med pleco to start them go from there. I've done this and females stay smaller and ( ime) can make a community setting that can be pretty diverse. I also had an angel in there and a keyhole and really never had any aggression issues.
I have a group of 6 young adult cutteri available, just found a small clutch of eggs when I cleaned the tank earlier tonight. They're closely related to convicts, but a little better-looking and not as overabundant.
I'd really like to move them along because they're sharing a tank with 8 Gymnogeophagus Norte that are also pairing off and spawning. I have a larger/older pair of cutteri in a 29 with a swarm of 7-week-old fry, and really don't want or need any more spawning pairs. You could keep a pair of them and swap off the extras for something else at your lfs. If you want them for $30 shipped Priority Mail shoot me a PM.
It's not the fact that you cant keep A convict, or A firemouth, or any number of small to medium cichlids, it's just that you want to avoid having breeding pairs unless the tank is huge, dedicated to just those fish.
So for example you could probably keep a convict, a firemouth, a blue gourami and a couple of Bristlenose plecos quite happily in that size tank and have a nice semi-aggressive community.
But a breeding pair of Convicts will OWN the tank.
I would include some bigger but more peaceful fish. I would try something like the "Geophagus" brasiliensis, Hypsophrys nicaraguensis, a firemouth, a blue acara and Archocentrus spilurus.
Jewels and Convicts don't mix in male/female pairs. Both breed like jack rabbits so theirs bound to be trouble. Plus full grown Jewels are more robust the convicts. The ones I breed are stone cold killers. Goodluck with that mix.