There's a book called The Boleyn King that I've seen recommended, in which Anne has a boy instead of Elizabeth.
LOVE the 'whatifs' about Katharine living longer, because it makes me go 'Ha, if you hadn't been so horrible to Katharine, you evil wanker, things might have turned out better for you and you wouldn't have ended up a great seething mass of self-pity about what bad luck you had with wives.'
My version, though, would involve Anne having to get someone else to father the child, because she might reckon that not having a healthy son was down to Henry rather than her. I don't actually think she committed adultery in RL, but it's an intriguing what-if. She could have picked Thomas Wyatt and we'd have had a king who was very good at poetry.