We can't very well tell you to read Jane Eyre (1847) without recommending Wide Sargasso Sea too. These novels may have been published over a hundred years apart, but they go together like peanut butter and chocolate.
Jean Rhys has a really cool way of following Charlotte Brontë's storyline while painting the Antoinette/Bertha/madwoman/misunderstood wife character in more detail than Brontë ever imagined. And, bonus: we don't just get Antoinette's side of the story; the whole middle part of the novel is narrated by her mopey husband himself.
So ask yourself this: does Antoinette actually suffer from mental illness, or is her behavior caused by the way Edward treats her? What are the stakes of letting both of them narrate a chunk of the novel?