Have you considered Glofish Tetras? My ex fiance got a pink one and it was near indestructible. They aren't especially large but they are much bigger than neons, cardinals, and others. Their body profile is almost like a silver dollar's. You can get them in green (awesome looking but maybe too bright if the attention isn't supposed to be on them), orange (more yellow than orange), pink, red (slightly pink), and blue. There are also long fin varieties. I have pictures of mine next to an angel somewhere, the tetra and the angel actually seemed to develop a bit of a bond and always swam side by side.