(Excuse the length; formatted it for readability.)
Your guesses are all good (and by "classics" I meant the works of Seneca, Cicero et al). You'll also find many gems in the bibliography section of any book with real substance. A good author will share their sources. On why I recommend these: Many of these researchers spent years grappling with the said topics. They are "invested" in it, and to be charitable, were/are trying to arrive at truth, however imperfectly. Even when they get things wrong, these books are more likely to make us think than the vapid "books" by charlatans.
On Thinking, Fast and slow being hard to read: it is a hard read. For Pete's sake, the book asks you to grapple with probabilities, which we humans are terrible at. If you're trying to read Prospect Theory (a key idea from the book) in bed when tired, or in a noisy train station, you will be frustrated. Read it when you are fresh and are able to concentrate well.
Note though, none of these books are "perfect"; there will be things in them that might irritate you. Read them anyway, for the mental nourishment they provide.
* * *
More broadly, if you're interested in psychology, primate behaviour, neuroscience, philosophy, game theory, and linguistics, here are a selection of books that I've found helpful:
• Descartes' Error by Antonio Damasio
• Neuroscience: Exploring the brain by Bear, Connors, and Paradiso (this is a fantastic illustrated text book with great explanations; fully worth the 72 euros I paid for it)
• Behave and Why Zebras Don't Get Ulcers by Sapolsky (I wrote my "why" for Behave here[1])
• Moral Tribes by Joshua Greene
• The Evolution of Cooperation by Robert Axelrod
• Chimpanzee Politics by Frans de Waal
• Homo Ludens: A Study of the Play-Element in Culture by Johan Huizinga
• Metaphors We Live By, George Lakoff and Mark Johnson
• Becoming Human by Michael Tomasello
• For Stoicism, I wrote a detailed guide here[2] on good quality English translations by foremost scholars
• Not least of all, read some of Plato's dialogues—they're immensely fun, even if you don't agree with anything he says. Here's[3] a few recommended English translations.
[1] https://news.ycombinator.com/item?id=25559890
[2] https://news.ycombinator.com/item?id=25559890
[3] https://news.ycombinator.com/item?id=27440236