2 Occe/Percula clowns
1 Flasher Wrasse (Paracheilinus Species, ie: Yellowfin, Linespot, McCosker, Carpender)
1 Pygmy Hawk
1 Tailspot Blenny
OR
2 Occe/Percula clowns
3 Flasher Wrasses, 1 Male & 2 Female (Paracheilinus Species)
I would go with the first lineup but the second can work if you have a bonded harem of 3 Flashers. They are pelagic and are known for jumping. I know from experience.
I would not recommend a Mandarin for a 37 gallon tank unless you have prior experience with them, your tank is heavily stocked with copepods, and you are persistent with your copepod replenishment. A single Mandarin will devour an entire self sustaining population in a 37 gallon in a month or less so they will need to be re-stocked.
I would not recommend Firefish with the Flashers or larger Fairy wrasses (Cirrhilabrus), because they frequently bully Dartfishes is small tanks. Firefish color and dorsal fin gestures look too similar to a Flasher wrasses competitor. Either the firefish or the wrasse and firefish will jump out of the tank from this behavior. Sometimes these two fish families (Dartfish and Reef Labrids) can get along but a 37 gallon stacks the odds against you.