What about (unfortunately my rep) Jim Cooper? He still has that "blue dog" appeal despite being reliably liberal on most issues. A drawback is that the Democratic Party would need to come up with a secession plan or scheme to move him to Cohen's seat in Memphis, since he is quite likely to be out of a seat in Nashville following 2020 redistricting since Nashville is D+7, but is surrounded entirely by TN-4, TN-6, and TN-7, which are all R+20 or so. There's no reason to expect anything other than four ~R+15 districts that contain pieces of Nashville.
Show me a map that would produce an 8-1 R delegation in Tennessee.