Question about replacing Clownfish

I have a 120 gallon reef tank which had 2 Clownfish, Royal Gramma,
Yellow Tang, and a Sailfin Tang. It also has some blue mushrooms.
Unfortunately about a week ago I lost one of the Clownfish. One was
very small, one big. The one I lost was the small dark colored
clownfish which I believe is male. Is that correct?
My question, how can I safely replace this clownfish? These are false
Percula. Will there were any problems with aggressiveness and as
well do I have to worry about getting a female or male when I replace
or will it choose the sex later? This has been a stable tank for
around 4 years with lots of live rock and no anemone at this time.