After sharing too much information the other day that was of no use to anyone, I want to make up for it today with some information that is actually useful.
I have one of these. It is called a Ma Roller and can be purchased in yoga stores or online. It is marketed as 'the Tool that gives you Very Deep Relaxation,' which strikes me as a slightly unfortunate word choice, but it really works.
Basically you lie on it and the wooden bulbs on each side of the dip push into your back on each side of your spine, using your own weight to apply gentle pressure.
It's wonderful. Totally cutting edge yet also ancient Chinese.