I wish you all the luck starting out on your new private class adventure! It can sometimes be very intimidating - even after doing it for years!
From my experience, most, if not all, of my private students prefer NOT to use a book. They appreciate the fact that I prepare my lessons using topics that are relevant to them. For example, I have two students who work in Human Resources. My cousin in the States happens to be an HR manager at a big company so I request training material from her that she uses with her own colleagues that I can use in class with my Brazilian students! You could also find tons of information about HR online by subscribing to newsletters and such. That's just for HR.
The other day, I had a new student who won a scholarship to Oxford, but he didn't know how to open a bank account in London. So the whole lesson was about doing just that. You can easily build a lesson and create a lot of great input for a learner by using sources that are interesting to them, and that don't necessarily come from a book.
Another tip: plan lessons that you can use with MANY different students. If you have 25 privates and you create lessons for each of them individually, you'll kill yourself! Find a topic that would be relevant to as many of them as possible - the protests in Brazil for example, and create lessons with that.
As for a book, I like the Cambridge Face2Face books. They have four different levels and some good, though not always relevant, topics.
I would also suggest you ask your students directly what kinds of things they would like study! They are the best sources for you for ideas to prepare your lessons.
Check back with them frequently about how they are enjoying the classes. Ask them! They will not say anything unless you ask them. Then you can tailor the classes to fit each individual better.
Good luck and let the community know how your classes are going!