This is an old 1983 book. But it is still the best book available that analysed how Montgomery planned the Normandy campaign, how the campaign unfolded, and the controversial decisions made during the campaign.
Much more than a narrative of events, this book is a thinking man’s book that delves deep into strategic and tactical issues in the Normandy campaign. Highly recommended.
For the most recent D daybook, I recommend Sand and Steel (2019) by Peter Caddick -Adams.