I would NOT get a tomato to replace the perculas, tomatoes are quite aggressive compared to percs.
You have a very nice mix of fish in there, maybe a goby would be nice? There are a wide variety of gobies out there, some are tank raised like neon gobies, just be sure to research the species first because some gobies have special needs. Or maybe a nice fairy wrasse? I just love fairy wrasses.
If you are set on replacing with another clown, the "clownfishes" book might be good to read before you decide. I know after I read it I wished I had room in my tank to try some different clown species. This is the book I was talking about: