Hello @Yunzi (is that you? — nice to “see” you here, too 
)
Hard for me to answer, because …
- I’m still hovering somewhere around 13k and 19k.
- I have too many books already, and I can’t bring myself to read any of these from front to end
- It’s quite hard for me to say which books are recommendable for which strength.
BUT here is what I recommend:
- Richard Bozulich – “The Second Book Of Go” (perhaps from 25k on?)
- Charles Matthews – “Shape Up! (For A Stylish Baduk)” (ditto)
And then I can recommend ALL books by Robert Jasiek that I’m reading in:
- Robert Jasiek – First Fundamentals
- Robert Jasiek – Fighting Fundamentals
- Robert Jasiek – Endgame 1 – Fundamentals
- Robert Jasiek – Easy Learning: Joseki
I’d say these latter books are good to read from perhaps 22k on (up to perhaps 5k or even higher?)
I believe Jasiek’s books have contributed to my ascent from perhaps 17k on. You might think that’s not a lot since now I’m between 13k and 11k, but I have been spending far too little time on Go study and play, and things like that I’d intermittently beaten a 6k and a 2k in correspondence games, and just recently a 4d in a 9x9 game, didn’t happen before, I’m QUITE sure all this would never have happened without the clearly structured and defined principles I learned from Jasiek’s books.