Alright this has me fascinated...
Have you ever thought of trying two of these:
https://www.amazon.com/dp/B07NLMCTWS...NsaWNrPXRydWU=
I mean I think there will be problems, but a pair of these beach balls would be a good start. You'd probably would have to make a custom article of clothing but I would think once enough air is placed into both the shape would be consistent with what you would want to achieve.
I also think somewhere at the Bearchive forum there is an actual thread on how to make an inflatable bra using a specific brand of latex children's toy (I cannot remember the name).
But yeah this sound super interesting.