I have the
LeatherZ Mark4 armrest and it works really well for me. It puts both my elbows at the same height making long trips more conformable. Plus it provides valuable extra storage. Some people say it gets in the way when shifting, but I don't find it gets in the way at all. I think short people may hit their elbow on it when shifting.
Just cut a block of foam the size of the armrest and place in the location and drive around with it for a few days and see how it feels.