I am a man with medium sized hands. I’ve been comfortable wearing my band for almost twenty years, though I don’t feel like my knuckles are particularly prominent. Mine seems to be 6mm width and 1.5mm height and feels neither delicate nor chunky. If you’re specifically going for an extra rounded look and feel, maybe just stay away from the 1mm.
Really though, if this is going to be for daily wear, buy it from a brick and mortar store that can do a proper fitting, or from someplace that will send you some brass testers or something, if that is even a thing. I know you can do it for eyeglasses.