There is an Open Source curriculum [0].This consists of: MOOCs, videos, pdfs, etc. It should provide you with a guide of what/where to study.

Neil Sainsbury posted their own list of books [1]

Alan Kennington provides a 10 steps learning mathematics[2]

Another source to get an overview of a topic [3]

[0] https://github.com/ossu/math

[1] https://www.neilwithdata.com/mathematics-self-learner

[2] http://www.geometry.org/tex/conc/mathlearn.html

[3] http://mathonline.wikidot.com/