Your title lends nicely to a discussion about making a clownfish into a pair. About the only sure method of ensuring the desired outcome is to cut the male in half, making a pair out of the one.
Because they can change sex, the male who was dominated by the jumpy female is now the dominant clownfish in the tank. Adding any other clownfish of any breed will result in a struggle for dominance between your male and the new fish. If you add a smaller fish, it is possible that you will add a small female who will almost certainly not be eager to give up her sex for the larger male and a battle will ensue. If you do add a smaller male, you still will have two fish who may fight for dominance or may just fight because they really don't like each other. Either way, you get a fight and guessing the outcome isn't as simple as just adding a smaller fish or a new fish and expecting the two to be able to get along.
It can work but if it will work is not predictable until the outcome is known.
Pairing the same species is said to be easier as each clown species has its own unique mating dance moves that indicate submission or dominance that each of the fish need to recognize in order for a relationship to work. If they don't recognize the dance done by the other fish, they may keep fighting each other until one or both fish are mortally wounded and the dance ends when the fish die. Starting with the same species should help with the two fish recognizing each others cues and signals so often folk recommend against cross species pairing.
As mentioned before, the other issue is that there is no guarantee that the fish you pick as the new mate for your current fish will actually work. Think of your mom picking your spouse. Her selection criteria may not fully suit those traits that you might look for in a mate. Same mathematical probabilities are at work with your selection of a new mate for your clownfish.
That said, picking a new mate isn't difficult it just isn't a sure thing. New fish almost always fight during introduction time and we need to be ready to react to however they decide to behave towards each other if the going gets to difficult.
