I don't know the name or product that you are referring to.
But if you're referring to a yoga ball, any one will do.
I have this one, the 55cm one.
http://www.power-systems.com/nav/clo...&Resist-A-Ball
What are you trying to achieve w/ your physique? I can help w/ tips and let you be aware of gimmicks (like the TrimSpa junk).