During the recent months, I had a back problem.
I had a comfortable chair and I had no problems when working at my desk. However, when I went to sleep, my back started to hurt immediately when I went to bed. Not very much, but it was uncomfortable and slightly alarming to experience this almost every evening.
For Christmas I got that big inflatable ball to sit on. The back pain went away, and I mean immediately.
Several weeks later, Kryspin used his lightning-fast claw to destroy the inflated balloon in 0.01 seconds (while I was sitting on it) and my back started hurting again.
With Kryspin out of the way, I could've used the inflatable ball again but I found something more stylish:
These special Spinalis chairs emulate the effect of inflatable sitting balls but you look a lot less like idiot when sitting on them. Again, all the pain disappeared immediately.
As you can see, you can order them from Slovenia but if you are from the Czech Republic, you can visit the Czech dealership and try sitting in the chairs before you order (it takes several weeks for the chair to arrive).
Note that the Czech dealership is not a shop in the classic sense. You have to make your appointment in advance, either through web form or using the phone number listed on their webpage.