In read parts of Murphys "Probabilistic Maschine Laearning" (vol 1) which is an update of an existing book in ML. It covers a broad range of topics also very recent developments. It also includes foundation topics such as probability, linear algebra, optimization. Also it is quite aligned with the Goodfellow book. I found it quite challenging at certain points. What helped a lot was to read a book on bayesian statistics. I used Think Bayes by Allen Downey for that (http://allendowney.github.io/ThinkBayes2/index.html)