Not sure if you've walked it already and my advice is too late, but for anyone thinking of doing the Way, I walked it at the start of August. I took the XT40 map (recommended by someone else on here) which I didn't end up needing but which was immensely reassuring to have, and the Rucksack Readers guide, which I found very helpful. With the route description in the guide I didn't need to refer to the map. I also found the guide a good read, and it might make a nice souvenir, I certainly intend to keep mine rather than ebay it.
http://www.rucsacs.com/books/west-highland-way/I turned 42 just after the Way. My mum gave me the guide when she heard I was going to walk the Way