Re: fat boy seat?
Build your own saddle. Make it to fit you and where/how you ride. Check a local upholstery supply outlet for foam and covering material. Either sew it yourself or have a pro stitch up the upholstery. It will make a fun Winter project and you'll be happier with it than anything you can buy.
Bicycle seats are made for pedaling and not for comfort. The seat is one area where your motorized bike is closer to a motorcycle. It needs a comfy place to park your rear end.
Age and Treachery Will Always Triumph
Over Youth and Skill & "Charlie Don't Ride"