A new chair, I had a gaming chair that killed my butt and back (was cheap and had it for 6 years) now I got a true ergonomic chair, and wow! I didn't think the difference would be as big as it is. I didn't want to sit by my computer because of the old chair. This one follows my body movement in the back so I can stretch and move without feeling restricted.
Here is a link to it, but I bought mine from a refurbish store that fix up office furnitures from companies and resell them so I got it for less than half the price and it is like new.
https://www.steelcase.com/products/office-chairs/think/
I got a chair from them about four ish years ago. It's nice to see companies that really, genuinely refurbish stuff. My chair has held up great and only came with a few cosmetic scratches on the back. Well worth the massive savings versus buying new!
I am with you 100%! Instead of buying a mid tier chair did we get a high tier chair for the same price. It is good for the environment, your wallet and your body, big win!