Kneeling chair - I use https://www.amazon.com/DRAGONN-Ergonomic-Kneeling-Adjustable-Office/dp/B073ZN7B52 (in fact, I have two of these :-).

Disclaimer #1: AFAIK there are no studies that show the benefits of a kneeling chair (but then, AFAIK there are also no studies that show the benefits of a standing desk). Still, the chair made a huge difference for me.

Disclaimer #2: To adjust and get used to the kneeling chair, I would start with just 30 minutes in the morning and 30 minutes in the afternoon and extending the time gradually over 1-2 weeks. Also - it is important that you do not lean forward (e.g. when using a keyboard or a mouse) - leaning forward would flex the lower back and might exacerbate back problems.

Disclaimer #3: A comfortable chair is only one part of a solution. Moving from time to tome and changing positions is important in general for lower back health (e.g. don't sit/kneel all the time - get up and walk around the room every 10-15 minutes and/or get for a longer walk after lunch). I highly recommend the "Back Mechanic" book by McGill: https://www.amazon.com/Back-Mechanic-Stuart-McGill-2015-09-30/dp/B01FKSGJYC/ref=sr_1_1?crid=2T3452809ELSY&dchild=1&keywords=back+mechanic+mcgill&qid=1617841459&sprefix=back+mechanic%2Cgarden%2C242&sr=8-1

We had an older style of this chair in my childhood home growing up, and I used to love it!

I somehow found several ways to get reasonably comfy sitting "incorrectly" on even that chair, which probably explains a lot....

Here's the desk ( https://www.amazon.com/dp/B07GDP9PW3?ref=ppx_pop_mob_ap_share ) and chair ( https://www.amazon.com/dp/B073ZN7B52?ref=ppx_pop_mob_ap_share) I got.