The best set of adjustable rings I've found is the one in the CB6k, but the cock tube is plastic, so it's fragile (it splits) and bad for long-term because hygiene. I'd love a metal bar cage with the ring system of the CBs, I'd buy that in a second. The metal rings must be usually fixed if you don't want pinching.
But since you say you are big, you could try with a fixed metal ring, the biggest you find (usually 50 mm for knockoffs)... my problem is the opposite: the 40 mm metal fixed rings are a bit too big. And I stay away from metal rings with hinges.
Maybe some other anon can help better than me.