What a great idea, Dee. Here's a tutorial on doing that exact project: http://sabbyinsuburbia.blogspot.com/2010/11/coffee-table-to-bench-tutorial.html
I would just upholster the top! I'd follow this tutorial - https://www.charlestoncrafted.com/2014/11/11/reupholster-seat/
Do you know first if the legs and the structure of the coffee table are strong enough to support weight if used as a bench?
O.K. That's good to hear.