It's best to read non-fiction long before you settle down to your story in such specifics. Because nothing else will teach you the questions you need to research.
Take two examples.
A writer was discussing world-building and asserted that a medieval king would never have been called the Sun King because the term would have had no meaning in a geocentric universe. groan. Plenty of ancient and medieval kings used solar imagery. "Now is the winter of our discontent. Made glorious summer by this son of York" is predicated on the actual use of the sun in War of the Roses heraldry. For one thing, the center of the universe was not a desirable place to be in the Ptolemaic universe, because it was also the bottom of the universe.
And a website was contrasting Japanese and American views of the kamikaze pilots. It spoke of how the Japanese saw the bright young men setting boldly out, and the Americans saw the destruction they inflicted. Erp. At that time, in the US, I know the Catholic Church routinely denied funerals to suicides; other denominations may have, and many that did allow funerals had only recently started it. Suicides were still papered over as "accident while cleaning a gun" to hide the shame, the horror, the disgrace. True, nobody insisted on burying suicides at the crossroads with a stake in their hearts to keep them from becoming vampires, but suicide was Not A Good Thing.
This is why you should read primary source, stuff actually written from all sorts of times and places. Some have a limited range of stuff, but there are no substitutes for reading them to realize that what you are taking for granted and should be researching. Secondary sources may suffer from the same blind spots as you do and not bother to draw them issues to your attention. Even -- perhaps especially -- those secondary sources that are out to show you how different people think; they often have axes audibly grinding about what examples they want you to notice and on what subject matters.