im in year 11 too, and from what i've read:
the silent patient by alex michaelides is SO GOOD
the maidens (by the same author is also really good and the plot twist is INSANE)
verity by coleen hoover- im not really a huge fan of her books like some but that specific book was pretty good
i probably have more on my books list spreadsheet but i read way more sad and like mentally raw books than i do thrillers (i've got a lot of recs of thriller books on my books list, but ive never gotten round to buying and reading them- if u want i can still send you a list, because from what ive read about them they are VERY good). but i hope that helps!!