Chastity gear recommendations for bigger guys

My guy and I are still at the stage of researching devices. My worry is buying a device that doesn’t fit right and throwing money away, but particularly (since it’s more what I want than him) having his first time be unpleasant so he backs off from the idea of MC. My biggest issue is sizing and comfort. After taking measurements as suggested by a well-known site, I feel he’ll need a bigger device. I’d prefer steel for its durability, but I’m unsure how to pick exactly the right one. It has to be comfortable yet stay put (obviously). Which makes or models work well for larger men? Personal experiences and reviews are welcome. Thanks in advance!