Here's your list of all the Agatha Raisin books in order, which ones the TV show has covered and what was changed.
The Book Blog of Evil: Introducing Agatha Raisin, by M.C. Beaton
Agatha Raisin Series in Order
All 30+ Agatha Raisin Books in Order by M.C. Beaton [Guide]
Agatha Raisin Mysteries Ser.: Kissing Christmas Goodbye by M. C. Beaton (2008, Mass Market) for sale online
The Confessions of an Agatha-holic: Bring on the Murders!
Where to Start with MC Beaton's Agatha Raisin Series
Agatha Raisin (TV series) - Wikipedia
The Walkers of Dembley: An Agatha Raisin Mystery [Agatha Raisin Mysteries, 4] 9781250093981
Busy Body: An Agatha Raisin Mystery (Agatha Raisin Mysteries #21)
Introducing Hamish Macbeth: Mysteries #1-3 by M. C. Beaton
All the Agatha Raisin books in order & what the TV show changed
Agatha Raisin and the Fairies of Fryfam book by M.C. Beaton
Agatha Raisin: An Intriguing Journey Through Mystery - TheWritersHQ