Ok. After ruminating on the problem and reviewing threads here on seat cushion replacement, I decided my driver's seat bottom cushion was somehow failing.
Going out on a limb, I ordered the new cushion from Gaudin Ford, aka SilverstateFORDparts.com
. I used the drill down parts finder on their site. Part # turned out to be 7S4Z54632A22A for a non-heated seat, driver's side 2007 compatible pad. John Michaels handled my order and stayed in communication.
The price for the cushion came to $80.59 (fdown rom $125 my dealer wanted) with $11.26 shipping = $91.85
I removed the bottom cushion "assembly" (cushion + metal tray) via four 10mm bolts -- without removing the entire seat itself. One electrical cord fastens to the bottom of the cushion tray with two clips -- easy enough to slide the cord out.
The old cover came off easily by snipping eighteen hog rings and removing three fastening strips along the sides and front of the cover.
I couldn't see much difference between the old and new cushion... however after a lot of examination, I could see the old cushion was slightly "torn" on the outboard side of the cushion -- the side opposite of where I was feeling the painful contact with the interior of the seat... what I know now was the metal tray. The inboard side of my seat had a sunken, feeling, and I could definitely feel the metal tray under the foam. I suppose the rip had something to do with the problem. New cushion installed = no problem.
Replacing the cover was actually much easier than I thought it would be -- using eighteen 4" zip ties, which I happened to have on hand.
I took the car for a test drive and the seat is now as it should be, problem solved.
I bought the car used with 13K miles, it now has 23K miles on it. I'm not overweight, I wonder if perhaps the previous owner might have been overweight -- otherwise I'm at a loss to explain why this happened.
Either way, the replacement process took under two hours -- very easy. If I find the threads I used to help do this job, I'll place links here, too.