Speaking as a BBW myself, I would recommend a draft or draft cross, which is what I should have bought in the first place. I am losing weight, but will be much to large to ride anything else for a very long time, if not permanently. I rode a bit this weekend and my very cruel daughter videoed the event.
That poor horse! It was a good thing I only rode him for a quick lap (just to show I could still ride after 20 years).