Route from Boston to Fort myers

You could try to drive straight from Boston to Pittsburgh the first day in about 9 hours:
https://www.trippy.com/distance/Boston-to-Pittsburgh
That gets you away from the coast, but bypasses NYC, Philly, and DC. Then do a more leisurely drive down to Fort Myers:
https://www.trippy.com/drive/Pittsburgh-to-Fort-Myers-FL
Really, once you get to North Carolina, I would probably head back toward the coast if you're not in a hurry and maybe stop by Wrightsville Beach and Myrtle Beach, but it really depends on how much time you have.
The other option is to bypass those major cities by just taking smaller roads to avoid the major traffic, but mostly staying on the main route. That would probably be faster if you're just looking to avoid the big city traffic.