A "Half Round Foam Roller" is indispensable to bring rear-arching flexibility to any part of the spine. Lie on it in bed after spending hours sitting. Have it placed against the lower spine. It can even be used lengthways along the entire spine. ... can also use it while driving.
Hmm, not sure how good that is. Pretty sure every fitness guru out there advises against using foam rollers for your lower back. Not sure why tho.
I actually got mine from a chiro - there must be a precise diameter required for the spine - 14.5cm hard foam.