If you're having issues keeping rummy nose alive you have a bigger problem that won't be solved with more fish.
In the past, I think I had my flow to high for the little buggers. Plus, the vent(intake slits) were to big and the fish would get pulled into the filter. I fixes those problems once, and still had fish dying.
I could give it another go but I dunno. I lost about 100$ in fish and don't want to do this again... I just wish I knew what was wrong.
I'd say ember tetras are pretty hardy. In fact, you rarely have a fish die nowadays if you put it in a cycled tank, regardless of pH, GH, KH, etc. This is because fish adapt really well to different parameters. I'd say try embers. My 10 year old cousin has some in her tank and they're really cool fish.
I'll look from them next time I am in the store.
Here is my list of possible tank mates:
5) Nerites Snails