One Ocellaris will do fine but the pair relationship adds to the tank, IMHO. I lost one of my Okes after about a year...the survivor had become the dominant one and I made the mistake of adding another that was too close in size to her.....she harassed the newcomer unmercifully and it didn't make it.

Armed with better info, I added a very small one and the older Clown took to it like a new puppy. They've been a happy pair ever since.
I would recommend getting a new Ocellaris, much smaller than the other one and enjoy them.
Dick)