I know you asked for books, but I have to mention the videos of Grant Sanderson (3Blue1Brown) [1].
His explanations of mathematics are the only ones I can think of that have given me the same sort of piercing clarity and insight that one gets from reading Feynman on physics.
I guess he's pretty popular around here, but if anyone still hasn't seen the channel, please check it out. if I could, I'd vote for this guy to get a nobel prize. seriously. education is critical to our future, and efforts like set an example that I personally consider to be invaluable on the long run. what I mean is that it's easy to recommend videos of people like this, but since it's "just a youtuber", we often fail to reflect more deeply about what's —at least in my opinion— an amazing contribution to humanity.
I agree that he's a great educator. I wonder if a book by him would work as well, though. A lot of his explanations depend on the animations he makes.
Maybe if schools and colleges had off-the-shelf software that was 80% as good at making explanatory animations as his Python lib is we would see a huge boost in the understanding of maths.
His explanations of mathematics are the only ones I can think of that have given me the same sort of piercing clarity and insight that one gets from reading Feynman on physics.
[1]: https://www.youtube.com/c/3blue1brown