At the risk of being wrong twice in the same day in the same thread I'm going to say Ocellaris
Is the one pictured the one that you lost? Can't really see the other one but I am going to continue my overconfidence and guess the pictured one was the male. If so I would get a small Occ. out of acommunity tank and you should be fine. Even in this situation you may see some chasing and aggression displays but not all-out death matches!
When I lost my male I did not replace him for months and when I did my female chased her new bo all over. Funny thing was she was never aggressive at all. She was chasing him because she was so happy. After about 5 minutes they were literally doing the clown dance in the corner of the tank. It was very cool.