Any pointers on useful textbooks in this space? I seem to have difficulties finding one that is at the right level (not too easy, not too hard) or that provides a way to gauge your level and start accordingly at a later chapter or whatever.

Depends on what you need, I suppose. This resource is said to be pretty good: https://www.susanrigetti.com/math

I decided start with Calculus I on MathAcademy because that was the last thing I did in High School. MathAcademy disagreed and told me to do PreCalculus and even bits of Algebra II first, but I knew better (MathAcademy was right and in hindsight I should’ve just started the Foundation courses to build up my pretty weak algebra skills again).

For Calculus I simply use the textbook that’s recommended at the link above. As far as I can tell, it’s good. I don’t do the problems, though - for that I use MathAcademy.

Not a textbook, but https://betterexplained.com is an awesome resource for gaining intuition, its author's approach is very unlike others I've encountered.

I'm biased, but very fond of the open-access introductory textbooks used where I studied. The department was very much pure maths, but the intro classes were accessible to general liberal arts students. I think the texts are relatively unique in that they're very proof oriented, yet with a pedagogical style that doesn't assume the reader is a future graduate student.

For calculus, three options to see if you like a particular author's style of explanation: http://people.reed.edu/~mayer/math111.html/math111.pdf - the most pedagogical http://people.reed.edu/~mayer/math111.html/math111.pdf - the most beautiful https://people.reed.edu/~jerry/111/calc.pdf - the most technical

For introduction to mathematical analysis and proof: http://people.reed.edu/~mayer/math112.html/math112.pdf

For multivariable calculus: https://www.stat.rice.edu/~dobelman/notes_papers/math/calcul... [1]

For linear algebra, we used the relatively standard Friedberg Insel and Spence [2], but I hear good things about https://hefferon.net/linearalgebra/.

[1] Link is off university domain, since apparently it was at some point turned into a bit more hardcore textbook oriented towards those going onto graduate studies in mathematics. If curious: https://www.amazon.com/Calculus-Analysis-Euclidean-Undergrad...

[2] https://www.amazon.com/Linear-Algebra-4th-Stephen-Friedberg/...

For proofs and introductory real analysis, I highly recommend Prof. Jay Cummings' books at the awesome price of about $20 on Amazon for freaking 400 page books. If anything, just buy it to support the guy.

I've been learning math from the ground up and I've gone to hell and back in terms of resources.

Art of Problem Solving is the best. I started with Prealgebra and it just flows. The best textbooks I have found.