The best office chair for your back should be one that can support your lower back and provide lumbar support. If you want something that can support the entirety of your back, a high back chair would be ideal.
Again, the best office chair back pain sufferers can be comfortable in would be an ergonomic chair because the design is specifically made to support the body of the users.
You should be fine with the Champion: Adjustable Ergonomic Mesh Back Office Chair with Foot Ring or the People’s Favorite: Hbada White Adjustable Office Chair.
You should also look into getting additional cushioning to make sure that your tailbone isn’t receiving the pressure from your upper body.
Another aspect you should look for in a chair is whether it can recline or if it can tilt. These features will allow you to lay back to stretch or rest your spine.