I love Altus Body Ball, but I got the weighted version and I love it! The ball has 2Lb of sand fill. It is ideal for using it as a chair because you do not have to chase the ball all over the places at your office. And you can easily do some exercises whenever you get a break from work. Also the added weight makes you work harder to move the ball with your core muscles and your legs. It is perfect for my need!
I have not seen any weighted version on Amazon because this is some new trend. So I post my comment here because the brand is the same and I am very satisfied with the quality of it.
To look for weighted version, take a look at Altus Body Ball package, the left bottom section should say "WEIGHTED BALL PROVIDES ADDED WORKOUT OPTIONS AND BALL WILL NOT ROLL AWAY" (The regular ball says "USE FOR CORE, STRENGTH,FLEXIBILITY, YOGA OR PILATES")