I've had occasional back problems over the years, and so I have a couple of professional quality ergonomically adjustable office chairs (they're the conventional kind you sit in or on, and you don't kneel or anything like that). The ones I have are something like
this, but I think they have more adjustments.
I would look for a chair like the above with as many adjustments as you can afford. You also might want to use on of
these to put your keyboard at the right level. I've found that sitting squarely in a properly adjusted chair makes all the difference for me.
BTW, I also spent some time adjusting my monitors and indirect lighting to reduce eyestrain.
See
this and
this.