I use the standard mouthpiece that comes with the Yamaha, but always remove the first 5mm of the top, which makes it much easier to play. I just file it down.
Alan, apart from a ‘one size fits all’ mouthpiece, could you be more specific about what you’re looking for in a mouthpiece? And why? Is it the shape? Or is it more to do with using a hose which doesn’t contain an elbow?
Then I’ll see if there’s anything I can think of!