Exercise Ball Recommendations

Hi,

I am looking for some recommendations for a decent exercise ball, as I need to get my core muscles kicked into touch! I had a c-section last year and I am struggling to do anything like sit ups. Someone advised an exercise ball is good.

It needs to be able to handle 22stone though, I must be the only person in the world to lose weight whilst pregnant and then pile it back on, plus more once the baby arrived!

Thank you