IME percs command a smaller territory than ocellaris clowns. A pair of percs would be perfect for your 12 gallon.
I don't think a true perc is any harder to keep than an ocellaris.
It has been said that the number of dorsal spines is a diffinitive identifier between A Ocellaris and A Percula..........but boy oh boy, have you ever tried to reason with a clown fish to stand still?