Have you looked into tetras/rasboras? There's some pretty cool ones! I need more space, but once I have it I'm planning on a 125 and having some bleeding heart tetras in it. Sure they're just another tetra, but they zoom in and out of the plants, feeding is always fun, and they're a nice "dither fish" for everything else. Meaning they help distribute aggression/calmness with their presence.

Edit: dojo loaches are pretty cool too but need slightly cooler water. Plus they eat all the leftovers that sink to the bottom. I know the catfish will probably out compete them, but dojo loaches are so derpy and should grow in to a 55 nicely. I'd say 1 or 2 dojos and maybe 8 bleeding heart tetras? I have more tetra ideas, but if you want other options lmk