Obviously, the history of Western philosophy includes thousands of books and to narrow it down to five is ridiculous. But I’ve chosen books that I think are incredibly important and not too threatening to read if you haven’t studied philosophy formally. These are books which are classics, undoubtedly, and repay reading at the level of ideas but have some kind of literary merit as well.
They’re all male authors, which reflects, sadly, the history of philosophy up until the 20th century, dramatically skewed towards male writers for all kinds of sociological reasons that have nothing to do with women’s ability or potential to write great philosophy.
The books is quite difficult in parts because of the 18th century prose, but it’s worth persevering with. It’s also very easy to find commentaries on Hume to help you through that, including an amazing website originally made by Jonathan Bennett called Early Modern Philosophy, which includes complete paraphrases of huge number of philosophical works in contemporary language, including Hume’s.