These are the best I have found over the years. I have three of these that are 20 years old. They get used every day by clients. They are still round, hold their air well, and a solid purchase.
They may be a bit more then people would expect, but Many of my clients have them and love them.
This is the Fitterfirst Dura ball Pro:
These are what I use. They are great and they last for ever.
I only had one client pop hers because she left it sitting next to the fireplace.
You need to get the right size:
People that are 5 feet 10 inches or taller should get the 75cm/30 inches
People that are 5 feet 5 inches to 5 feet 10 inches should get the 65cm/25 inchs
People that are 5 feet 4 inches and below should get the 55cm/21 inches
Here is an Amazon link for you to buy one for yourself.
Make sure to look at all the drop down windows for all the different types of products that I recommend.