In my experience, as other commenters have mentioned, Khan Academy is pretty decent and constantly embiggening its resources.
From what I've seen, Brilliant.org is good in higher-level maths, but I do not have personal experience that I can use to vouch for it.
In my Discrete Math, Beginning-level Engineering, and C++ programming classes, I use Zybooks.
Zybooks is very interactive and tells you how to do the problems in ways to where one can actually understand why things occur the way they do - in contrast to the typical textbook approach where they provide methods that never seem to be helpful (to me at least).
Here's a Zybooks book catalog. Yearly subscription is around $50 USD - much more affordable than $120+ for a physical textbook that you use one time in your life.
If you want to keep notes since it's a subscription, I recommend the Snipping Tool (should already be installed on your computer) in addition to Google Docs/Ctrl+C/Ctrl+V.
I agree with others about getting a tutor to assess where you're currently at, and where to advance, but I personally feel that a long-term personal tutor for continuous learning will probably not accomplish what you're seeking.
I love learning and I've learned that the most difficult thing to self-learning is knowing what words to use to search (usually esoteric language...), which is where the temporary tutor should help you a significant amount.
E.g. "How does electricity work?" versus "What is the difference between Wattage and Amperage?". The latter quotes will give you significantly broader and more helpful information.
Lastly, not only are Wikipedia pages helpful for info through the articles themselves and the sources listed at the bottom, but the articles usually have many hyperlinks of prerequisite/corequisite topics that can lead you down to what you need to know.
Don't forget about YouTube and public PDFs that some universities post online.
In summation: Khan Academy, Brilliant, Zybooks, a tutor only to assess current knowledge and what else there is to learn (so you can get those keywords to use for self teaching), Wikipedia (article, in-text references, sources), YouTube, university PDFs