For your last big trip I don't know I'd do either LBL or ST. Unfortunately, I haven't gotten to hike much in the area yet, but there aren't a whole lot of choices as you say in this portion of the Midwest for week-long treks. I did this map for a Scouting project. Links to all the state and national forests where you can find info on trails.
Unless you don't have the gear, I wouldn't worry about going north. Seems like lots of decent areas in the UP. Record low for Isle Royale in June is 28. May be too late to plan a trip there, but shouldn't be much chance of any snow unlike the Rockies.
If you prefer warmer, perhaps the Ozark Trail. It appears you're not concerned about a shuttle. My other suggestions in order of distance would be Red River Gorge, Big South Fork, Smokies (but designated sites so you could AT near there) or Dolly Sods/New River Gorge.
I'd recommend you give your son a budget and set him loose on planning where he's like to take his dad. :)