Mysteries have a zillion subgenres. Fenris seems to be using “cozy” to mean a “fair play” mystery, where the reader gets all the clues. Cozy has a different meaning these days, usually a small town setting with a woman as the detective. Those may or may not be fair play. Sometimes the murderer is trapped into confessing, or intuition plays a big part, or a surprise reveal is the ending. This was often true even back in the so-called Golden Age. Fair play went up its own ass with plots so complicated and preposterous that they drove away more readers than they gained. Hake Talbot’s Rim of the Pit is on every list of best classic mysteries and the NSA and Google combined couldn’t follow the plot. Anthony Boucher’s The Case of the Seven Sneezes contains nine crimes committed by four people. Clayton Rawson’s masterpiece Death from a Top Hat goes through seven different explanations of the impossible crime.
But mysteries also include police procedurals, private eyes of various boilednesses, crime novels, caper novels, suspense and horror, serial killers, spies and other types of thrillers, and things starring cats.
A few older favorites that I think might fit cozy plus atmosphere.
John Dickson Carr is the king of the impossible crime novel. He had two detectives, Dr. Gideon Fell and Sir Henry Merrivale, but their plots are interchangeable. Setting is between wars Britain, upper class but definitely not Downtown Abbey. Merrivale has more humor than Fell, but he’s written lightly as well. Skip the post-war books unless you get hooked. (The Merrivale books were originally published as by Carter Dickson but they’ve all be re-released under Carr.)
The short story parallel is Ed Hoch. He wrote more than 100 stories about Connecticut small-town Dr. Sam Hawthorne. Every one is an impossible crime mystery. No writer in history ever did more. Astoundingly, he wrote them in chronological order so that he could highlight the changes from year to year in the community. Obviously, start with the first collection, Diagnosis: Impossible.
Phoebe Taylor Atwood also had two detectives, Asey Mayo of Cape Cod and Leonidas Witherall of the Boston suburbs, with Witherall playing as farces. Skip the early 30s Mayo while she’s figuring things out. He changed a lot over the years. The stories set during WWII have an interesting look at the home front. (The Witherall books were originally published as Alice Tilton but they’ve all been re-released under Taylor.)
Craig Rice set her (yes, her) books in a Front Page-era Chicago with enough booze to kill Nick and Nora Charles. They are the closest thing to screwball comedy in print. Yes, I have a thing for funny mysteries, which are rare. But if they hold up they often read better than the supposedly serious ones.
Peter Dickinson, who died recently, won every award imaginable for his first five mysteries, each about Superintendent Pibble. Then he got better.
As for Edmund Crispin, he’s mostly post-war, set in England’s university community. His The Moving Toyshop is a classic, but I’ve read it four times and still can’t figure out how they got away with it. (A body is found in a toyshop but when they come back the next morning it’s a grocery store.) A better writer than most.