These three listed above are introductory books on the Norman Conquest that I can recommend. While the first two ([Garnett 2009]; [Morris 2018 (2016)]) is really readable concise work, my favorite, [Thomas 2008], approaches the Conquest from more wider points of view.
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If you are really, really interested in this topic:
- Bates, David. William the Conqueror. New Haven: Yale UP, 2017: This formidable volume is the latest standard of the academic biography of William the Conqueror. If you wish to explore the topic further in-depth, I also recommend to check his other books at the library (or online).
- Chibnall, Marjorie. The Debate on the Norman Conquest. Manchester: Manchester UP,
20191999: is, exactly speaking, not the book on the Norman Conquest itself, but on the history of scholars' discussions (historiography) in the 19th and 20th century. How they interpret/ give significance to the Conquest and how it changed by the end of the 20th century is the main topic of the book.
- Morris, Marc. The Norman Conquest: The Battle of Hastings and the Fall of Anglo-Saxon England. New York: Pegasus Book, 2012: includes detailed discussion on the extant sources and possible reconstruction of the events.
(Edited): corrects the publishing year of Chibnall's book (thus, the book does not covers the histriography in the 21th century. sorry).