As for Arthurian history, the much-maligned "Age of Arthur" by John Morris from the early 70's is still, I think, indispensable reading for the layman, due to the clarity of writing and the assemblage of source material contained therein.
Professional historians made an anathema of John Morris because he put far too much weight and credence on some legendary material, rather than having a minimalist, skeptical approach to the purported sources of Arthurian times.
But,
knowing that, the lay reader may still enjoy a book where the author is intimately familiar with all the sources we possesses (excluding archeological material accrued after the book's release), and see an
image of a society that the sources
suggest, although Morris have unwarrantedly eliminated other equally possible, and in some cases, more probable interpretations.
We do not
know the time period 350-650 AD as well as Morris thinks, but his book retains a value as evoking, on basis of the scraps of evidence we have, a society that might-have-been, an enjoyable historical romance if you wish to be hyperskeptical.
It might be juxtaposed by reading Alcock's "Arthur's Britain", a book I don't remember whether I've read..
A more detective-like, lighter book is "King Arthur: The true story" by Keatman&Phillips who thinks they have established who Arthur REALLY was.
As a reminder, the only almost contemporary account surviving from Arthur's own time is Gildas' "De Excidio" from the mid 6th-ventury, a work chastising the British princes of his day for being engrossed in personal vices&rivalry, rather than unifying against the Saxon threats, along with a slight historical account of how the evil state of Britain has come about.
Although neither Arthur or the princes he chastises is named, it is fair to regard the time when he grew up (the 510s and 520s) as the historical basis for "Pax Arthuriana", because he tells how much better things were back then, when the old king reigned (the Battle of Badon is typically dated to about 490 AD, when Arthur won the crown).
Of course, throughout all time, grumpy old men have ALWAYS romanticized the times of their own youth, but when Gildas is specifically mentioning the orderliness and more city-based society back then that was in the time of his old age, we may regard his time as an unravelling of a previously comparatively richer time.
Not the least because from archaelogy, we know that just during this time, commerce in luxury goods with Gaul and Spain flourished in the south-eastern parts of Britain (say, from Cornwall through Bath and southern Wales).