Office chair recommendations?

I’m a 5’2” curvy lady and I’m pretty sure my current computer chair (a cute one from Ikea) is partly to blame for my back pain. I have SI joint irritation/inflammation, anterior and lateral pelvic tilt, and functional lumbar scoliosis.

I already use a footstool so that my feet aren’t dangling but it’s not ideal. I think the cushion is too hard for my bum which is leading to pain in my pelvis and surrounding areas.

Anyone have recommendations? I can’t adjust my desk height, only my chair and footstool.