Yep, as Karl stated, we do it ourselves, based on our own knowledge (we're both former Paras), and research prior to the tour to identify where to go and what to see regarding specific events.
For example, I am currently reading "Battle for the Bocage - Normandy 1944" by Tim Saunders (Published by Pen & Sword, widely available, including Amazon) in order to learn more about the fighting, particularly armoured actions, on the left (east) flank in the countryside south and east of the bridgehead around and beyond Caen, and this excellent book will hopefully provide details and locations of specific actions, allowing us to visit some of the relevant places armed with the knowledge of what took place and when, etc.
Karl is also studying some other books for the same reason.
We do, however, refer to the battlefield guide books (as shown in last year's tour coverage) when/if required, along with current area maps, dedicated "D-Day" visitor maps and, where available, period maps (or facsimiles) and location and aerial photos produced at the time.
Some "tour guide" videos can be found online, some very good, some good, some reasonable (and a number ill informed utter rubbish !!), with the better selections from Al Murray and James Holland in their "Walking the Ground" series, along with those from Paul Woodage ( a Brit registered tour guide living in Normandy), and another chap who's name escapes me, but I think might be under the title "Wayfarer" or something similar.
These are particularly useful for those with little or no knowledge of D-Day and beyond, with some detailed coverage of individual actions/battles, including lesser-known actions, and these were useful in providing part of the basis for our itinerary last year.
Although we intend to visit a couple or more of the (numerous) museums we didn't get to last year, our aim this year is to see more inland locations, away from the "tourist" areas, mostly along the beaches, that many visitors (innocently) believe is the only place where anything happened, and, having a little more time to tour around this year, we can hopefully cover a lot more ground - and take a lot more photos too !