We've used the tennis ball trick too. Also, a water weenie can be used to roll on and as a spot support when at a chair. Or, you can slice it in half longwise for a chair spot support.

The Homedics massager is less than $40. They go on sale frequently if you watch Walgreens ads and such..

In my experience, the tennis ball just works the soft tissue. The Homedics massager can be put against the bones and cause them to vibrate allowing the muscles to pull them into proper placement. Sort of a chiro adjustment. I have a rib that gets out of joint where it attaches to the vertebra. This helps it settle back into place.