Start with a knockoff cage because they are cheaper and generally come with a few ring sizes to find one that fits you best! They won't generally be as comfy as official cages but help you know the size that fits you best. Vaseline on the inside of the cage and around the ring also helps with comfort. When caged also make sure to tug your balls and adjust the skin so things sit right and don't bunch up. Usually once I lock the cage on I spend a few minutes adjusting everything until it feels fine.

Biggrr tubes also aren't always better. Try to use one that is around your flaccid size so you aren't growing to fill it out. Thst just makes it uncomfortable. Too small at first may not be comfy either as getting hard makes the ring tug the back of your balls. Takes a bit to find what's comfiest. House of Denial ships from the UK and has some good knockoffs to start and a measuring guide!