This concern and the one about developing back problems are both great reasons to ease into using an exercise/yoga/stability ball as your primary chair. When people ask me about it, I recommend they start out with 20-30 minutes and slowly work their way up from there.

It's also important to get a ball of the right size (they typically are available in 10cm increments, with 55-75cm being the more common sizes). Look for charts online for sizing info, and then make sure it is inflated enough that when you're sitting on it the angle of your knees is 90 degrees.

While this change has helped my posture, increased my core strength and more, I think my next change is going to be for a treadmill desk so that I can increase the number of calories I burn throughout the day.

Same thing here, tried it at home for a couple of months then switched back to a chair.