You know what, maybe a stupid question, but have you been to a physio with your spine? It seems to me that a comfortable chair can make the problems even worse, because it takes your attention away from the real ones like too much muscle tension e.g. due to stress or other similar things.
Higher models of chairs mainly offer better workmanship, e.g. high-end synthetics instead of eco leather and many adjustment options, but in terms of comfort it's best that you sit on it. In general, chairs do not improve the situation with the spine, although having more adjustability is easier to set it under you. As I wrote, a very comfortable chair can at most hide back problems temporarily, but the solution most often is to introduce some exercises or change some habits. So if you want a comfortable chair, I'm afraid you have to sit on it, the price I would not suggest