Hi @Kaedalus! I’m also from south america (Brasil) and I’ve also learned english by “osmosis”, mostly by watching tv/movies, playing games, and reading a lot, so I think we have a similar background with this.
But here is the thing, I think I was first introduced to english at school with an age of maybe 7-8 years, maybe earlier, and I was finally confortable with the language by the time I was 18-19. So that’s 10+ years to learn a language “organically”, that is, without any real focus or effort in studying it. Looking back now, that doesn’t sound very efficient, but I can’t really complain since learning was just a side effect of having fun.
So how to do this with japanese? One method is called 多読 or intensive reading, and it has two objectives:
1-help you memorize grammar points and vocab
2-teach you new vocab through context
The material should be appropriate for your level, but there’s a very convenient thing called graded reader, which can be found in this post
The graded reader is designed in a way that it uses limited grammar and vocab which should be appropriate to your level, and it’s also written in a way that you can guess the meaning of the words through the context. It also feels amazing to read a whole text in japanese and understand everything without really needing a dictionary. So I say give it a go and see if those grammar points finally stick to your head!
PS: the NHK easy news it’s closer to a N3 rating, so it actually has an intermediate level of grammar!