The other thing to note is that the distinction between primary and secondary sources in political philosophy is a little different to that in e.g. history. Philosophy often develops through a critique and synthesis of other authors. Which means that a primary source of one author may also be a secondary source for another.

Consider Marx, Poverty of Philosophy, for example. It is a primary source for Marx and a secondary source for Proudhon.

There are still guide-type textbooks that are more like secondary sources, with everything simplified and predigested. I'm not a huge fan of these.

Then there are works by people like Alasdair MacIntyre and Bernard Williams. These are good at introducing philosophy because they're largely aimed at undergraduates. But they also criticise others and tell you what they think; i.e. they present their own philosophy at the same time. In e.g. Williams' Ethics and the Limits of Philosophy or his book on Descartes, you can see how he arrives at his own philosophy. These kinds of books are far more interesting, in my view.

Personally, I'd read something by Williams or MacIntyre and see how you get on. Have a look at their bibliographies and see if anything looks interesting. It doesn't have to be these two. Many modern academic philosophers will have similar books, chapters, articles. There are these kinds of compilations, too: https://onlinelibrary.wiley.com/doi/book/10.1002/9781405177245 (I assume you'll be sailing the high seas as these books are expensive).

Or read some of these: https://plato.stanford.edu/search/searcher.py?query=Political+philosophy

As for primary works, JS Mill is easier to read than Bentham. Hayek is quite clear. Aristotle isn't as difficult as you might think (depending on the translation). Machiavelli's Prince is quite short. Just search for the major political philosophers, read whatever comes up, and see how you get on. Or read something that I've linked and keep a note of people whose ideas sound interesting, and search for them. It will be a challenge but it becomes manageable if you stick with it.