Hi Fisher, first thing I would check is the nitrates in the tank, if they are high do a water change and see if it helps.
Second I would feed some raw peas. You can buy them frozen, zap them in the microwave for about 10 seconds and peel them. Feed the peas to the fish and see what happens after a couple of days.
Third could just be genetics sometimes their air sacs cannot take the pressure of being compacted or short bodied. I have a cool looking calico short-bodied oranda (looks like a comet that hit a wall head on moving at 80 miles an hour) that has been a floater since I got him. He will sit up at the top of the tank up side down for hours and never move from there. The only thing that I worry about is he develops any soars on his belly from being exposed to the air. I would put him down. Besides that he is a happy and healthy goldfish that floats upside down.
Avoxo