Hey there. have you ever looked into kribensis? they are quite a stunning fish at times, and are easy to sex and breed. they can be semi - agressive when breeding, but not too bad. usually quite nice fish. I have a breeding pair in with angels and other semi aggressive cichlids and they all get on fine. Kribs also dont get too big, maxing out around 5-6cm usually.
Another option which isnt so colourful but are still lovely fish are Keyhole Cichlids. keyholes are awesome, very placid little fish. Once again, easyish to sex, and easyish to breed. Get on with other fish well, just a little bit territorial when wanting to breed - not bad though, wont harm your other fish.As i said though, the keyholes arent colourful, striking fish, but are lovely and lively. They also max out around 5-6cm.
I have a pair of kribs, and a pair of keyholes, in a tank with 6 angels, and they all get on fine
HTH