As a longtime fan of Philip Pullman's work, I can confidently say that the 'His Dark Materials' trilogy, which follows Lyra's adventures, consists of three main books. The series begins with 'Northern Lights' (published as 'The Golden Compass' in the US), continues with 'The Subtle Knife,' and concludes with 'The Amber Spyglass.' These books weave a rich tapestry of fantasy, philosophy, and adventure, exploring themes like destiny, free will, and the nature of consciousness. Pullman also wrote companion novels like 'Lyra’s Oxford' and 'Once Upon a Time in the North,' but these are shorter works that expand the universe rather than being part of the core trilogy.
For those diving into the series, the three main books offer a complete and satisfying narrative arc. The depth of world-building and character development is extraordinary, making it a must-read for fantasy lovers. If you’re craving more after finishing the trilogy, the companion books and the newer 'The Book of Dust' series are excellent follow-ups, but they’re separate from Lyra’s original journey.