Although he was better known as a writer of Science Fiction, Isaac Asimov wrote a series of suprisingly excellent history books.
They were originally intended for a junior high school / high school Freshmen and Sophomore level of reading when they were written in the 1960s but I would put their reading level today at Freshmen college level.
Asimov was a professional scientist before becoming a writer; he does take some jabs at organized religion and Christianity in his books, but I still strongly recommend them.
I also strongly recommend them even though they are older books. They are a good introduction to the medieval period and would give you a good understanding of the period.
Each book also contains many interesting historical facts about Western culture and usually a timeline at the back.
The Dark Ages
The Shaping of England
The Shaping of France
Constantinople: The Forgotten Empire
Asimov wrote other books in the series about ancient civilizations: Roman Empire, the Near East, Greece and also about American History.
You can probably find some of them in most public libraries (often in the Juvenile section of the library); a larger public library in a wealthy community would probably have more.
Amazon.com sells some of the Asimov series but they are out of print and they want $80.00 for some of them, and while these are well written and interesting books, I wouldn’t recommend paying that price for them. I would pay around $20 or $25 maximum.
I also recommend:
The Devil’s Horsemen: The Mongol Invasion of Europe by James Chambers.