most of the fish sold in pet shops are fairly young and not at their adult size. That's how people end up with monsters in their tanks. Shubunkins will get to a good size. The fancy goldfish like orandas, ryukins, and telescope eyes get about 6-8". The celestial (bubble) eyes generally don't get above 5-6". You COULD fit one in a ten gallon, but you would be fully, if not a bit over, stocked. Also, you've heard right, their eyes are very delicate and sharp decor could rip the skin.
The general rule of thumb around here for the fancy goldfish is 20 gallons for the first, and ten for every following fish. Some sites will tell you you can fit any fancy goldfish in a ten gallon, ultimately that's up to you, but if you do go that route, at least over filter the tank to keep the water from going foul. Goldies are messy little buggers.
Shubunkins can reach 8" and will also be active, so would need a fairly large tank if you were to keep them indoors rather than a pond, especially when you consider that goldies are very social fish and like the company of their own kind.
For commons (feeder goldfish) and comets who can get anywhere from 1-2 feet, and are very active, a pond is your best best.