I would recommend these videos. A German documentary with subtitles and this: https://youtu.be/97hfRcrYBtE https://youtu.be/Y2jiQXI6nrE

The Martian's Daughter. A Memoir

not definitive but an interesting read from his daughter, quite an accomplished person in her own right.

While probably not "definitive" or even specifically about von Neumann, Turing's Cathedral by George Dyson had a lot of info about him and follows his work in computing, physics, and mathematics over the course of his career.

Martians of Science: Five Physicists Who Changed the Twentieth Century - Istvan Hargittai