When I started driving my mini, I made a mistake and bought a fairly cheap biothane harness, thinking everything was fine. I never hitched it, because I couldn’t stand the feel of the biothane - it just felt cheap.
I ended up buying this harness:
http://www.comfyfitharness.com/
And I love it on my mini. I think I would get one for my full sized mare if I ever tried to drive her. I took measurements and sent those on and it made sure the harness fit him. Thank goodness it fit my new mini as well. The betathane feels almost like leather and is padded in strategic places.