I recommend his autobiography: Life on Air. Even more, I recommend the audiobook, narrated by him.
There are some lovely snippets about his childhood, and his wife was clearly as lovely as he is.
It's also a fascinating history of the development of television and filming techniques.
I remember one of his anecdotes: One of his earlier series was in the preliminary process of being sold to a USA TV network. The network wanted to use an actor to dub over his narration.
Fortunately, there was a clause in Sir David's contract that meant he could veto that, which he did. Later, another network (possibly PBS) paid for the series for much less money, but with his voice. Although aired on a minor channel, the ratings were high. And when the DVD, with his voice, was released, it had the highest sales for a non-fiction series in the USA at that time.
So, he's not only our greatest national asset, he's probably a very significant export asset as well. 