Suggestions for new fish?

Definitely get more pristella tetras, they are schooling fish. You can try bottom feeders like kuli loaches, pictus catfish, plecos, corydoras catfish, or otocinclus. For other fish you can try angelfish (with caution will eat small tetras), a male betta or a combination of females, another school of tetras, gouramis (one per tank), swordtails, platies, barbs, and other small peaceful fish.