What is the opinion of Reddit about the
Ergonomic Kneeling Chair Adjustable Stool with Thick Foam Cushions and Smooth Gliding Casters for Home, White?

Have you tried those kneeling chairs? Ergonomic Kneeling Chair Adjustable Stool with Thick Foam Cushions and Smooth Gliding Casters for Home, White https://www.amazon.com/dp/B08CH1CGB1/ref=cm_sw_r_cp_api_glt_i_TBTBAZ8CFNZT44D8YPG8

Also I know of several people who sit on a yoga ball at the desk for this reason

I love this chair: https://smile.amazon.com/gp/product/B08CH1CGB1/

A cheaper alternative is to get a pillow like this: https://smile.amazon.com/bonmedico-Wedge-Cushion/dp/B07LH2ZJ2X/ and put it on top of your existing chair.

If you find either of those products helpful I suggest you try looking into this surgery: https://www.reddit.com/r/chiari/comments/ll3cep/sectioning_of_the_filum_terminale_an_alternative/ since that implies your entire spine may be involved in your condition