Thank you Amateur, hadn't thought of checking out human exercise balls. Will do that.Its just a cheap everyday exercise ball for humans that we had laying around - so really light and soft.
I made sure it was pumped up as much as possible to avoid the dogs getting a tooth into it. If its really full because of its diametre its hard for them to get their mouth on it - so far so good.
As for getting it under control - Ha ! I thrive on chaos !