Same experience. I like to rotate between 2 chairs, sometimes standing up, sometimes laying down. I still have mild back pain sometimes, but it's way better than what it used to be. I used to barely be able to sleep through it.

If you are suffering from back pain caused by sitting and have trouble sleeping, I used this video [1] to relieve the pain for a while. It helped so much that after 2-3 weeks of doing it every day 2-3 times, I was able to sleep normally again. I also slept on the ground for a while since my mattress was too soft. I now own a very firm mattress.

[1] https://www.youtube.com/watch?v=CO3racIlTcg