A new client told me about Body Rolling, she used it when she wanted to work on her own muscles and connective tissue. I had heard of using a foam roller, but this is different and less painful. The Ultimate Body Rolling Workout by Yamuna Zake and Stephanie Golden shows how to roll on a ball to release your back, hamstrings (heavenly!), neck, chest, abdomen, pretty much anywhere you feel tight. More importantly, the author focuses on creating alignment with the routines so you stand taller and straighter.
It uses a soft ball, like the ones you buy at a toy store not fully inflated (the frog ball above was a fun find that I use regularly), or you can purchase specially made balls from the Body Rolling company.
I had been rolling on a ball to work the tight spots out of my arms -- after all I can't see a structural integrator every week -- and the principle is the same. It's also similar to undulation in that your body is moving slowly and developing internal awareness. The difference is that your body weight creates more the resistance against the ball.
Body Rolling requires more flexibility and range of motion that most undulations and it includes the arms and legs, while undulation focuses more on the spine. I think this is a good next-step if you like undulations and want to go deeper. The author also has another book that is more technical and written for bodyworkers and manual therapists.