Another of the mystery series I really liked were the "Mrs. Pollifax" books by Dorothy Gilman. They weren't really mysteries so much as they were "cozy" spy novels. Emily Pollifax was a widow in her 60s who ended up recruited as a CIA agent. the series includes a delightful cast of recurring characters and there's a nice freindship that grows between Mrs. Pollifax and a young agent she works with.
Gilman was named a "Grand Master" by the Mystery Writers of America in 2010, two years before she died. She also wrote a slew of other mysteries. I've read some but none of them engaged me as much as the Pollifax series. Rosalind Russell starred in a movie version of The Unexpected Mrs. Pollifax, and Angela Lansbury starred in a TV-movie version. I think the series would make a dandy television series, kind of a Scarecrow and Mrs. King for an older audience. (Or put it another way, Murder, She Wrote with an international setting.) The books might be a little old-fashioned and cozy for today's readers but I loved them.