You may be surprised to find that more than just your chair is affecting your back. For example, the standard height of almost every desk you'll get in the US

You may be surprised to find that more than just your chair is affecting your back. For example, the standard height of almost every desk you'll get in the US is 29.5". This is just about perfect for someone who's 6 ft tall. If, like me, you are shorter than that, a proportionally shorter desk will change the way you use your chair. Similarly, when I started using a split keyboard, this obviously increased the comfort in my shoulders and upper back, but everything is connected and I feel like it was a good move for even my lower back. As far as chairs specifically, I picked up a Herman Miller Mira from a used furniture warehouse. It was still pricey, but for me it was worth it. I was able to get the lumbar support just right, and I'll sometimes adjust it through multiple positions throughout the day, because it is easy to do without even getting out of the chair. I would definitely figure out the proper height for your desk. I needed to go down to 26" in order to have my arms resting comfortably without having my chair pushed too high.