That's a tough one. One of the toilets that tends to get recommended for this situation is one of the Caroma line. THey have the largest trapway diameter in the industry (at least from what I can find)...about 3", where more common ones are 2-1/4" or even slightly less.
Another thought is one of the pressure assisted toilets...they have a storage tank under pressure that produces the jet to get the flush started. That jet doesn't last long, and might not last long enough to break all of a long stool apart. This is where the larger outlet pathway in the Caroma comes into play. It's much easier to get a longer, harder stool around and through a path when it is larger in diameter.