Tank Mates for my Jack Dempsey Cichlid?

I have a 4 inch jack dempsey cichlid in my 30X12X18 fish tank. It's been there for about 3 years. I feel like its lonely and im going to completely redecorate my tank. I don't feed it feeder fish so i don't know if it's aggressive or not (im considering feeding him rosy red minnows. why or why not feed them feeders? Im still deciding). when he eats the cichlid pellets, he jumps like a shark and attacks his food. i will eventually move him to a 55 gallon tank but for now he'll stay in my 29 gallon until he gets to about 6+ inches. but anyways, what tankmates would be good and how big should they be? I think he's sad. I originally bought an albino oscar with the jack dempsey but the oscar died 1-2 months after.