I've been doing the McDougall plan for 22 days and I can tell it's working for my severe RA. I just realized that I had better get a book in case I'm getting any details wrong (like I think I'm eating too much salt). Which book do I need or does it matter? I don't need to be convinced about the science and I don't really need to lose weight (5'7 female, 138 lbs) but I want whatever version is best for people needing to get healthy as fast as possible.
Congrats Lesliec1 on such a great start!
Hands down, start with Starch Solution
as it is simple guide reinforced by multiple chapters of specific points to underscore all the benefits of this dietary approach. It's a very nutrient-dense book in terms of information to support your direction.
Other than that, I recommend you read as many as you can as you move forward. Repeated visitations and reference to these materials clarifies your personal practice of principles and keeps you moving forward. All things McDougall are worth a purchase or check-out at the library, and don't forget Esselstyn materials, Doug Lisle resources, Neal Barnard, T. Colin Campbell's China Study - these are all worth at least an annual read to keep you on track.