Lost one clownfish from a pair - how to replace?

[Gort]

I've had a pair of clowns in my Solana since early February - added at the same time; one slightly larger than the other. The mis-barred black O - the larger and more aggressive fish of the pair so possibly female (?) - somehow made it into the rear filtration section of the AIO. I found it out of the water on a shelf.

They almost always "hung out" together and I enjoyed having a pair, so I'm interested in replacing the lost fish. What are the caveats I should be aware of? Should it be larger or smaller than the Ocellaris already in the tank?

 

[Somethings Fishy]

i not the expert but i would put a smaller one in the tank so it will be recessive, i am interested to see if it really matters