Well, in a 6 gallon tank, there isn't a large selection. 6 gallons would be much too small for a CAE, though. Your could try some shrimp, snails, or a pair of African Dwarf Frogs.
Edit: Forgot you still had two glofish there. Don't add anything else, it's already a bit overstocked.
Puck (Yellow koi HM king) / Scar (White HM) / Salt 'n Pepper (Silver HMPK) / 'That fish' (Copper butterfly HM) / No name (White DT) / No name 2 (Turquoise/white marble HM) / No name 3 (Lilac HM)
Bo Peep (Cambodian VT) / Goldilocks (Yellow VT) / Joie de Vivre (Multicolour VT) / Lil' Peep (Blue VT) / No name (Dalmatian VT) / No name 2