Yamuna recommends the Total Body Kits as the place to start. (There are Silver and Gold Ball Beginner Kits). The Gold Ball is a great beginning ball for people who are not yet used to body work or don’t like intensity, have osteoporosis, etc. The Gold Ball is also my go-to all around ball of the larger balls.
This program covers the hamstrings, each side of the spine up into the neck and scull, the abdominal area, the chest, and the shoulders from the front. It is good foundational work in YBR and is a great general workout for keeping the body well aligned, toned, flexible, and with high quality range of motion.
If you have specific issues – try the other kits, or contact me for a private (online or in person). I have online videos to follow, after consultation.