Adult books don't have to be steamy whatsoever. There's a whole women's lit genre that more than just romantic fiction. It's real life stories. I mean look at the book Me before You. The main character is 27 and there's very little 'steam' in the entire book, yet I found it to be engaging and emotional. For real if a book is only steam with no substance, that's boring.

Focus on your characters. Who are they? Why are they doing what they're doing? What things happen to mess them up? People read books for the characters, not the plot.