I am very fond of the novels by the British author, Nevil Shute. They are long. They are not written in easy English. But they are not written in difficult English. Most of them are positive in tone and have happy endings. They often involve protagonists who make long, complicated, quest-like journeys. Here are several of my favorites:
1) "The Trustee from the Toolroom"
2) "A Town like Alice"
3) "The Chequer Board"
His most famous novel is "On the Beach," but I don't think it's his best, I don't like it much... and it does not end happily.