I just ordered one of these:
They have a slightly smaller model covered with a "velour-like cover" that would probably feel nicer than vinyl but I sat in the van with a tape measure and really think I need quite a bit of added height. My usual "comfortable driving"position is with my elbow on the arm rest and hand on the side of the wheel. I have to lean over in the seat just to get my arm to touch the arm rest right now. (At least I can angle the inside one up higher.)
Should be here by Friday, then I can test it over the weekend when I drive a couple hours out of town.
This isn't just a Ford issue though. My Nissan NV200 also has a completely useless armrest - in the opposite direction. Rather than have a level window sill it slopes up front-to-back so that where my elbow would normally rest is nearly as high as my shoulder.