I had sciatica for most of my life until a couple years ago when I had hip replacement surgery.
I have a really old Herman Miller I think is the brand. I paid $500 for it in 1994. I was measured for it. It was sold by a local office furniture store. Not Staples or any of those but a store that designs interior spaces like office cabinetry, etc. It is literally designed to fit my behind--well actually my lumbar curve. Best 500 I have ever spent. I don't think they do that any more though.
19 years later and I still use that chair. Can't say that about the cheaper ones.