If you have the time to read detailed WW2 airwar histories, the Shores/Cull books are pretty definitive about Malta, and other theatres. There are also many books written about Beurling.
An interesting Spitfire pilot's-eye view is Dennis Barnham's "One Man's Window," c.1956 (William Kimber) and reprinted in the 80's in paperback.
When you find one book you like, check its bibliography for the source books the author used, and then find and read those. Rare books can be found fast through abebooks.com.