Start with high-confidence history of religion books, then narrow by subgenre or adjacent topics.
The Book of Saints
Jo Rose
A History of God
Karen Armstrong
Trent
John W. O'Malley, John W. O'Malley
Seven Men and Seven Women
Eric Metaxas
Amazons of Black Sparta, 2nd Edition
Stanley B. Alpern
The Divine Library
Rufus C. Camphausen
Paul and Jesus
James D. Tabor
Turning Points
Mark A. Noll, David Komline
The Divine Office in Anglo-saxon England, 597-c.1000
Jesse D. Billett