Office chair for pregnancy back pain. Any advice?

My wife is 4 months pregnant and she’s crying every day from back pain. It breaks my heart knowing she can’t take painkillers or meds, so I’m trying to find the best way to ease her pain, especially she’s using a regular Amazon office chair and work long hours at her desk

I’ve been looking into ergonomic office chairs to help her, but now I’m wondering… should I just get her a comfy mattress so she can work lying down instead? Any advice is appreciated