If you want another laterally compressed fish maybe a smaller butterfly might fit you. Hopefully the angel takes it well.
You could add more wrasses. Basslets, pair of Clowns, some not too feisty damsels, Cardinals, would all be options. A Borbonius (try to get captive bred) or Sunburst Anthias. Marine Betta (try to get captive bred). Dartfish. Keep one of the Tangs.
My centerpiece of choice for a 90gal would be one the fish mentioned or a pair, maybe harem of dwarf angels.