Jill Paton Walsh has written four Lord Peter Wimsey mysteries.
The first, Thrones, Dominations, is a completion of a partial manuscript left unfinished when Sayers turned to translating Dante and other interests. It deals with the very early married life of Harriet and Peter, the time just before WWII, the brief reign of Edward VIII, and murder amid the fashionable theatrical and social scene.
The second, A Presumption of Death, is a wartime mystery; Harriet and the children are staying at Talboys to get out of the London dangers, and it's full of the wartime atmosphere. Walsh used some wartime pamphlets Sayers wrote to get some of the atmosphere, but did not, I think, get any of the plot from Sayers.
The third, The Attenbury Emeralds, combines a reprise of Peter's early case (never described in full by Sayers) with a current mystery involving the same gems. It takes place shortly post-war.
The fourth, The Late Scholar, is new to me; I just saw it in Fantastic Fiction. It takes place in Oxford.
Any Sayers fan will want to read them. They're a pretty good job, keeping the spirit of the Sayers stories, and reasonable mysteries. Of course a Sayers fan has quibbles, but they are still very good reads.
I won't give spoilers by saying how the personal life of the characters develops, but I think you'll be interested.