I think I ought to mention to you there's an apparently quite fun new French movie featuring him and Auguste Macquet (with Depardieu, playing Dumas as I understand, though perhaps it's Macquet. The whole cast is apparently stellar.).

It's not a biography as such, more a window on some episodes of Dumas' life (there's been a lot of movies like this from France recently, the Molière one was especially funny. Instead of a bio, they took an episode of his life where he "vanished" from historical records, right before he started writing his most famous comedies, and invented him an adventure in which he met the people and situations that would inspire him his plays. Hilarious)

The reviewer this morning was saying the movie was as entertaining as, and felt very much like, a Dumas novel.

That sounds like you sort of things