I use beachballs since I'm a child. They are cheap, easy to find and durable. Yes they can be poped ( ripped open ) but it take a lot of stress to rip them! There is many brands and qualities. For the sizes, it's all about what you you want to do. Two small ones for some breat inflation, a medium to large size for a belly inflation, a big to mega size fo the body inflation and if you want to go to the extreme and if you have help, many sizes and on in every limbs and on your body and go fully inflated. But trust me you will be totally helpless.
I use for my belly inflation a 26' beachball ball. I get a really huge belly
For what I call body inflation I use a 48'' beachball. I could get a bigger beachball but I think I would need a bigger suit.
Once inflated to the size you want, you can close the beachball valve and stay fully inflated for hours if you want. They are pretty strong that someone could bounce ride on you while you are fully inflated. I did it and its fun.
My advice, if you can, buy a few. For back up in case;)
48'' beachballs
26'' beachballs
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