A Ball Chair is a "room within a room" with a cozy and calm athmosphere, protecting outside noises and giving a private space for relaxing or having a phonecall. Turning around its own axis on the base the view to the outer space is variable for the user and thus he is not completely excluded from world outside.
I have found it helpful to do the stretching exercises my physical therapist recommends. Do some core strengthening exercises, such as the ones highlighted at The Mayo Clinic. By keeping your core strong, your back won't put itself in a position to cause that sciatica pain you are having.