Visited the Tower last week. No need to book in advance. We bought our tickets directly from the on site ticket office, next available time slot was an hour later which gave us time to visit the Cathedral and the Ballistero. We had a wait time of 10 mins only. Cost 18 euro, 300 steps, you are allowed about 35 mins to get up to the top ,have a look around and get back down. The view at the top is hampered by the safety meshing so don't count on getting great photos. Worth the money, probably not but the experience was good.
If you own or manage Leaning Tower of Pisa, register now for free tools to enhance your listing, attract new reviews, and respond to reviewers.