I had some kind of lower back soft tissue injury about fifteen years ago and couldn't remotely comfortably sit on a 'normal' chair for more than a few minutes. I tried kneeling seats too and have two of them from a company which was Stokke and now seems to be Varier Furniture. The critical thing for me, if you try one, is to use one of the moving ones. i.e. the ones which are effectively a rocking chair, particularly when working at a desk using a computer, for example. For me it's the movement which is as important as the partially kneeling posture.
http://www.varierfurniture.com/en_gb/Movement-ChairsFrom the above page, I have the sixth and seventh items down (Varia Balans and Thatsit Balans). The first of those has vertical adjustment, but doesn't rock and it's good for a situation where you're regularly getting up and moving around. The second one is really comfortable for long periods (hours) as it's highly mobile and you can lean back onto the back support occasionally, stretch, etc.
They are far from inexpensive, however. That said, they are very well made and mine are as good as new after well over a decade. Perhaps experimenting with a cheap one to start with is the way to go; see if it helps and whether the kneeling position suits you? After knowing that, the ability to rock/move is needed for long periods of use, I found, at which point I suspect cheap ones are going to feel flimsy and not last overly long.
