Generally speaking there is no such thing as fact when it comes to historiography. Every work is influenced by the information available to its authors, their perspectives and biases, and even the time in which it is written. There are works which have more historical merit than others, but that doesn't mean these works won't be supplanted by subsequent work down the road.

I'll take the example of the Roman Empire. For a long time, Gibbon was considered the definitive English-language text to the layman. Every gentleman worth his salt would have read The Decline and Fall the Roman Empire. Today, we accept neither his observations nor his conclusions. Not only that, Gibbon is arguably responsible for the comparative dearth of quality English-language scholarship on the Eastern Roman Empire because of how dismissively he painted its thousand-year history. This began to change in the 20th century, but the predominant view of the Byzantines in a post-Gibbon world was that of a shadow of Rome's old self, a long history of decadence and decline.

Where does this leave us today? An accessible layman's history of the fall of the Western Roman Empire and its aftermath might be something like Wickham's The Inheritance of Rome: Illuminating the Dark Ages, but it really only starts in 400 CE and doesn't give much coverage to the factors which led into Rome's fifth-century decline. It's still quite worth a read if the subject interests you--I would call it the ideal text for an undergraduate course on the early Middle Ages based on where the literature sits currently. Ward-Perkins' The Fall of Rome and End of Civilization comes also to mind to focus more clearly on the fall itself, but I don't think it covers the aftermath as well. So unfortunately no real one stop shop.

In summary no, there is no perfect book. There are books that are better than others and the best way you can figure this out is to look up how the work was reviewed in academic journals. But history is an ever-evolving field and one of the most rewarding aspects of it is seeing how new information and new perspectives can reshape our understanding of the events of the past.

Vanished Kingdoms: The History of Half-Forgotten Europe by Professor Norman Davies could be the sort of thing you after.

“Europe's history is littered with kingdoms, duchies, empires and republics which have now disappeared but which were once fixtures on the map of their age. What happened to the once-great Mediterranean 'Empire of Aragon'? Where did the half-forgotten kingdoms of Burgundy go? Which current nations will one day become a distant memory too? This original and enthralling book peers through the cracks of history to discover the stories of lost realms across the centuries”