I’ve also read some of the suggestions above. The Laundry series can go more grimdark than the Peter Grant books, especially as the series continues and everything gets more apocalyptic.
I read 2 or 3 of Benedict Jacka’s Alex Versus books, but they didn’t hook me. They feel a bit more pulpy than the Peter Grant or Laundry books.
I have really enjoyed all the Kate Griffin books, though it took a while before I got into the first one (A Madness of Angels). They’re probably more similar in tone to the Laundry books than the Peter Grant books.
KB Spengler’s Rachel Peng books are set in the universe of the A Girl And Her Fed web comic. I got into the books from the comics and I enjoy both. The comic and the books probably do strike a similar tone to Ben Aaronovitch’s work.
As others have said, you should probably read stuff like Neverwhere, American Gods and Good Omens if you haven’t. China Mieville’s work can be pretty bleak but that is usually more in his Bas Lag novels than in a lot of his other stuff. Be prepared to be well aware of his politics by the end of reading one of his books. 😉
If you’re happy to look at older stuff, Michael Marshall Smith’s sci-fi novels – Only Forward, Spares and One of Us – could work for you.
Other things you could try include Nick Harkaway’s The Gone Away World and Angelmaker. They mix humour, seriousness and action. I really enjoyed both of them but got stuck on the next one of his I tried, Tigerman. Also Robert Jackson Bennett’s City of Stairs, City of Blades and City of Miracles trilogy is good fun too.
I am currently stuck somewhere in Rotherweird.