So I decided to give my derrière the benefit of the painful doubt and bought
The Dynair ball cushion (to give it its proper name) is made out of some kind of thick, durable, floppy rubber filled with air. It works like a normal cushion but it also exercises your muscles, even the tiniest movements make your back compensate the wobble motion. I'd recommended to everyone who has to sit down for hours on end at a desk. It's not expensive (I paid 40€) and you can claim it back tax wise (ergonomic back strengthening office stuff). I've got the 33cm version, I was taken aback a little because of the size (I thought it would fit into my hangbag, but it's slightly bigger than the entire bag). I have one of those Avolites 'From Rock to Opera' messenger bags and it fits handsomely in there. And I still have some room left for an A4 binder and my box of sandwiches.
So I'm taking this Togu thing everywhere I go from now on. (And yes it does sound like something a vegetarian might eat).There is one little snag. I feel like I'm wearing the hat with the tall feathers in the Muppet sketch. Those who come and sit behind will know what I am talking about.
And if people inquire why on earth I'm sitting on a frisbee I usually have to mention in passing it is not for hemorrhoids.
I've also discovered an advantage, though it might only be me. Sometimes the chairs are too low to adopt a good hight for typing. I get shoulder aches and tennis elbow from having to work in that strained position. I can adopt a more relaxed stance now, even when I'm just at our kitchen table having dinner.
And I just like to stand out from the crowd too. I like to feel special.