OK, so here are my recommendations for quantum mechanics:

To start yourself on a gentle but not devoid of substance course in quantum mechanics, I can point you to this course on edx: Quantum Mechanics for Everyone (audited it, there are moments to gripe about, but it's not a bad place to start). If you prefer books, I remember Quantum Mechanics: The Theoretical Minimum (associated lecture series can be found here. Returning to Classical Mechanics will help you get used to Lagrange and Hamilton formalisms, important as QM and QFT don't exist without those two) by L. Susskind and A. Friedman rather fondly.

Going through those should be more than enough to make books like Principles of Quantum Mechanics by Shankar easy. That's the textbook my undergrad QM course used in conjunction with Sakurai and Landau-Lifshitz texts. The latter two are more in-depth and advanced, but they complement the course really well.

For special relativity refresher, I can recommend this course by Brian Greene. It's interactive, problem-based and feels complementary to most textbooks.

Immortal all-purpose recommendations would be Berkeley course in physics and Feynman's Lectures.