Your Dovii should go in that 120 by himself, but in a year or two you will need a large tank to support him.
I wouldn't recommend any other fish to go in a tank with a dovii, a Pleco may be the only other fish able to go in.
I keep a Pleco with my Dovii aswell.
My Pleco is very active though, my Dovii just doesn't like anything else.
Not Dovii's, not Barbs, not Cichlids lol.