The fish you have are carnivors so if you want to stay in that family try a Royal Gramma.
Besides a small angle you could try a Blenny. I have a tailspot.
What's your pod population looking like? Your tank SHOULD be big enough for a mandarin and if you can get one that's been trained to accept other foods, you would be in good shape.
Besides that a royal gramma or some sort of dottyback would work.
I wouldn't go with the DottyBack, agressive and territorial fish with a mean punch. Known to fight off fish three times it's size.
How long as your tank been set-up for ?
twin spot hog, peppermint hog, yasa goby, randals goby, 2-3 blue eye cardinalls... if you plan it carefully and keep on top of your tank you should be able to fit more than one fish in there