I probably should not be making any suggestions as I have not yet kept this fish so am not 100% sure if it would be similar to what you're looking for.
What about a brown ghost knife (apteronotus leptorhynchus)? It may be a bit smaller actually than what you'd want (have not been able to find a consistent max size) and I've heard they're shy but perhaps having the tank to itself and with time it would become less so? I imagine you may be able to hand feed it as well since most can do that with the black ones.
Why not another FH? Just curious, don't answer that if you don't want to.