You might be best planning your own tour then, and arranging local guides at key sites of interest.
So, perhaps start by picking a theme for your trip. Next, work out some of the key places to visit for that theme. For those, find out if there are guides there, and if the free ones will be enough (eg at Bletchley Park you might find the free guides enough, unless you're really into your Crypto). Book additional guides / private tours for those where you'll want more.
With that in place, work out how to get between the sites, and then find other less known WW2 sites / museums / locations roughly on those paths. Finally, book local guides there, perhaps via the local tourist information office or a local historical society.
That might require a little bit more planning than just pulling out a credit card and booking onto a group tour, but I suspect you'll have a much better experience! There's a fair chance that your best experience will be with some local historical buff guiding somewhere who really knows their stuff, and who shows you things you'd never have thought of!