If you want hardier fish, I would go with an apisto of some sort over a ram. Angels are hardy once they get some size on them, but small angels tend to be very delicate.
A different direction for a 55g tank is tiger barbs, golden wonder killis, bnp, and a rainbow shark.
If you want a peaceful community, there are tons of cories, platys, Pristella tetras, bloodfin tetras, red-eyed tetras, silver-tip tetras, lemon tetras, bnp, black skirt tetras, and white cloud mountain minnows which all are usually pretty hardy and would do fine in a newly established tank.
There are tons of other options too. I wouldn't be overly concerned about a fish being particularly hardy though as long as you do your part with the pwc and tank maintenance, but I can understand if you just want to avoid overly sensitive fish.