Rainbow cichlids are a great shout — I’ve had them with cories and danios before and they held their own without being pushy. If you're leaning toward a peaceful setup and possibly a small group of keyholes, that's a solid direction too. I've found keyholes to be very chill even when breeding — they do guard their spot, but it's more of a "gentle warning" than full-on aggression.
Have you considered apistos as an alternative? Some of the more mellow species like A. borellii could fit the vibe and bring some interesting behavior to the lower zones of the tank.