If you want a horse that can do pretty much anything, and has a big butt, you might want to look at Haflingers. They tend to be quite strong very manuverable, and also have a tendency to be quite smart, which can be good and bad. Anke, my Haflinger, kept taking her halter off somehow, even when tightened. I still have no clue how she did that. They tend rather calm too. On a recent trail ride, she knocked down a rotten tree, and really didn't react. They do tend to mature rather slowly, so seeing a green broke 5 or 6 year old would not be an indicator of trouble, necessarily.
These two might be worth a look, though the pics of the second aren't that great.
Dandy Bella Luna