Reddit mentions of 160 Eight-Measure Exercises, Op. 821: Schirmer Library of Classics Volume 147 Piano Technique

My suggestions are going to be very simple. I highly recommend you don't try to skip anything thinking it's too easy for where you are. This is how you end up with lots of gaps. I speak from deeply personal experience and some of the best improvements in my playing have come from realizing that unless it's easy enough that I can sightread it perfectly and effortlessly the first time, it's worth working. Every small thing even in children's beginner books helps build that scaffolding that remove ability gaps and helps you be a better and more consistent player.

>1) get some classic stuff that we learn at the begining and

Not entirely clear about what you want in terms of if you just want the basics or you specifically mean you want some classical style stuff. Either way, here are some recommendations.

Alfred All-In-One - This is just a generally good book to work through with a lot of fairly basic stuff mostly sticking to a very small harmonic palette used in a ton of music. You can carry on to level 2 and 3 when you're done.

Masterwork Classics - If you're looking for actual simple literature, this is a great place to start. Very easy pieces and a great progressive series of books.

Burgmuller Op. 100 - Probably a it more challenging, but great progressive stuff as well and very classical.

Czerny Op. 139 - More progressive goodness.

Czerny Op. 821 - Not progressive, but lots of very short, bite-sized exercises that isolate specific things that show up in classical music, but in a fun musical way rather than just dull exercises.

>2) get better at sight-reading. I have lots of gaps in my piano skills.

Progressive Sightreading - These are ridiculously easy, but this is really where you should start. They are easy enough to let you be successful quickly and focus on keeping your eyes on the page because they are all within a 5 finger pattern reach covering all keys.

Paul Harris books - These are progressive sets of books that slowly introduce specific concepts. My favorite part about them is the articulations and stylistic directions that go beyond just having you hit the right notes, but have you actually thinking about how you want a piece to sound.

Mikrokosmos - These start a bit easy, but get hard very quickly. They also tend to not stick to predictable western harmony, which helps with getting your reading out of its comfort zone. Additionally, there tends to be a good deal more left hand motion and even melodies which really helps your left hand not just be the accompaniment hand.

Bach Chorales - I'm honestly not a huge fan, but some people swear by these. I would actually instead recommend finding a hymnal instead. These chorales are not only more difficult than most hymns, but will be extremely frustrating if you don't have a comfortable 10th.

In general, you should be learning lots of small pieces constantly. A huge part of sightreading is actually being technically capable. If you can't execute it technically, you can't read it. So find lots of pieces in a variety of styles that you can learn in no more than a week, or better, several of in a week. Lots of short focused pieces will chip away at very small weakness in your playing very quickly and efficiently. This will make your reading much better. Better technique and reading will lead to you being able to learn increasingly difficult music much faster. You'll likely find that something that once might've taken you a month to learn could be learned in a week. Something that could be learned in a week might be learned in a day or even sightread.

Try to remember when learning new, simple pieces, to try to keep your eyes on the page. Not matter how slow or out of tempo you need to go, really learn to trust your ability to feel the distances and shapes of chords you need to play. You might need to look early on for stuff that is more difficult for you, but try to get to a point where you don't need to look. When you can trust yourself in that regard, your reading ability will increase a ton.