I used Overlord and took their Omaha and Utah Beach all day tour. I thought it was excellent. Military history is one of my interests - I've done coursework as well as hobby interest. I hadn't been to these beaches since the 1980s (we self-toured) and wanted to return to see the newer museums. I thought the tour info might not add anything to my store of knowledge and experience, but I was wrong. The guide was excellent - lots of info specific to the sites we visited, stories of individual soldiers, etc. My tour was not primarily an overview of the battle plans, logistics, and campaign - much more specific to the spot where we stood which I appreciated. Very well organized. Several couples on my 8 person van had taken another tour the day before with the company and raved about that experience as well.
I know others have recommendations for different excellent private guides and tour groups. My sense is that there is a lot of excellent guiding going on on the Beaches. I walked by several other groups and could monitor some of the interactions!
I visited the Caen War Memorial via train from Bayeux. No need for a guide, very fine exhibits. The taxi driver who took me from the station to the Memorial recommended that I stroll around William the Conqueror's castle, so I did that before catching a return train. I'm glad I did - there is a small Normandy Museum that I enjoyed and a small art museum with a collection that surprised me in quality. (I am a museum person..... Others might simply enjoy walking around Caen a bit. Several old churches, vibrant shopping area, etc) There is easy bus and tram transport from the train station to the War Memorial and in central Caen - I used a taxi on arrival because it was there and I wanted to save time. Driving to the War Memorial would be easy.
Discoveries from Amboise base - I spent a morning exploring Tours before catching the train to Chenonceaux. Very interesting medieval city center to wander. The Compagnonnage Museum had been recommended to me - French organization of craftsmen and artisans dating from the Middle Ages. I found it quite interesting with historical tools, examples of past and current workmanship, general history of the organization which still exists in France. No similar organizations in the US that I am familiar with. The website might give an idea to determine if what is there is of interest. 30 - 45 minute stop would be enough time to see the exhibits. French language explanations, with English brochure available. https://www.museecompagnonnage.fr
In Amboise, in addition to Clos Luce and the Chateau Royale, I visited Château Gaillard. A smaller building, newer addition to the chateaux viewing options. Very helpful staff - I enjoyed my visit. The reviews are mixed - some think it is overpriced. There are some trails above the chateau that I explored, so I felt that I got my money's worth! I wouldn't rank this stop as as important as Chambord, Chenonceau, or some of the other chateaux stops, I just had the time to wander over from Clos Luce. The gardens are of historic interest - first orangery in France, prominent original designer. https://www.touraineloirevalley.co.uk/royal-estate-of-chateau-gaillard/ and https://www.touraineloirevalley.co.uk/cultural-heritage/chateau-gaillard-amboise/
I would recommend the audio tour, slight extra fee, for Blois Royal Chateau if you stop there. There is an included iPad (Histopad) device that several of the chateaux use, but I found these a bit heavy to carry around and not as easy to use as the audio guide at Blois which looked like a large pen. I've never seen anything like it elsewhere - I'll have to keep looking! The audio background on the architecture was excellent as was the history and stories of several of the royal residents.
When are you traveling? I wish you a great trip!!