Buying a new office chair

I am a 44-year-old woman with low back problems and recently bought your book on my mom's recommendation.  I can already tell it is going to change my life!  Thank you so much.  I am due for a new office chair at work and want to get one in line with your principals.  The back of the book mentions a pdf about chairs but I haven't been able to find it on your web site.  Do you have a summary or description of what kind of office chair is best?  If not, I'll just go by the general principals discussed in the book about chairs.  Thanks!