Could it be possible to improve and learn all of it without entering to a conservatoire or a "official" school?
. What I really want is to improve my technique, to remember the basic and play the pieces I want, Chopin's especially, to open wider my perspective in music. I want to have the piano level I should have until now.
What you need is a really good teacher. That's not cheap either, but it's less expensive than paying for a degree you don't need and won't use.