Adding another clownfish

I have a 36 gallon saltwater tank. I currently have 1 clownfish who is doing just fine. I started my tank off with 2 clownfish not knowing what really could happen. I bought a larger clown and a smaller clown. The 2 clowns got along fine for the first few weeks. After a while the larger clown would swim into the smaller clown, nip at it's fins, and get very territorial. The small clown had destroyed fins and was now staying in a small area of the tank and if it left he would get attacked. I figure this was just them trying to decide their sex as most likely they were not both female as the smaller one never fought back. After 3 months of having them both the smaller one passed away. It's been over a month now since the small one died and I was thinking about getting a new fish. I'm was thinking a royal gramma. Would this work or could this end up badly as my clown seems to be territorial. If you have any suggestions on a fish I can get, any comments regarding my idea of getting a fish, or if you would like to share a story regarding this topic please submit your reply! Thanks! :)