you mean the famous genre "cozy mistery"? Agatha Christie for sure, most direct descendant from Conan-Doyle.
Have you read all the other Sherlock Holmes books? Yes, they are all in the public domain. You may find free copies
everywhere, except on Amazon where they usually charge 2 dollars for any ebook, even public domain classics...
BTW, after I read on Holmes first book, A study in Scarlet -- where Watson mentions past works in the detective genre, most notably Poe's Auguste Dupin -- I immediately went on to check out those. So I read the first one -- The murders in the Rue Morgue -- but while interesting as a precursor, turned out too bizarre and inaccurate for current tastes. I heard The Purloined Letter is arguably the best out of the 3 Dupin stories and am looking forward for that...