New to corporate life and in pain

I got a new job about a month ago and it’s my first office job. I’ve worked in retail for the past decade, I’m very used to being on my feet and only really needed to be at a desk during uni, but even then it was never this stationary.

I’m fairly fit (regular rock climber) and have good core/back strength, but the pain from sitting all day is becoming a problem. I’m doing all the right things ie frequent walk/movement breaks, trying to align my body to my workstation correctly etc but it’s not enough.

Theyve given me an Ikea Millberget chair which was apparently crafted by the devil himself. After a lot of complaining, they’ve agreed to budget $200 for a new chair for me. I doubt this would cover what I’d need so I’m willing to pay out of pocket (I wanna keep my spine healthy for as long as I can).

I also fractured my tailbone a few years ago which gives me a fair bit of discomfort on some classic saddle stools I’ve sat on. I haven’t investigated what the issue is but it’s on the list.

If you have any recommendations to help this gal out (170cm, 55kg, real pretzel-type sitter) I’d so very much appreciate it!