Gaiam Total Body Balance Ball Kit, Blue, 65cm

I bought this for my 3rd trimester of pregnancy and am so glad. It is my favorite place to sit now - helps with my back and my hips. Don't think you can skip the step of giving it 24 hours after first inflation and then pumping again; it really does expand more. The little measuring tape that came with it helped a lot. Only caveat is that the plug is really hard to get out - I bent up a pair of tweezers removing the plug to repump. Well worth the money, even without looking at any of the linked exercises.

Besides my own that I bought years ago to help with my knees, I have now bought two purple balance balls for two children ages 4/5 years old. Both kids loved playing with the big balls. They lay on them, push them along with their arms or their legs or do cartwheels from them. In other words, they just love playing with them and get lots of exercise doing so. The only problem I have had with the balls is that they tend to lose air. I am thinking I may not have the plug in them securely enough. So, I do have to re-inflate them to keep them at maximum size.