Myler Bits

http://rods.com/p/5022,130_myler-cyprum-correction-kimberwick-bit-by-toklat.html
I know NOTHING about english riding but this looks like a fairly helpful page on the kimberwicke.
From what i've read the bit is legal but frowned upon because it shows that the horse is stubborn/hard to stop. I'm not sure if you can but have you tried a good snaffle? I know for western i use a Tom Thumb which is a rather severe leverage bit that you need VERY light hands to use. Also is only to be used on a trained horse.
 
Also from what i've read pelham is used as a leverage bit and it sounds like thats what you need. Just remember to be easy on the mouth.( with any bit)

I have the loose ring french link by myler and I'm quit pleased with it. Though my horse doesn't like bits, he seems to like or at least tolerate this one.
I believe some, but not all, are legal for shows, but I know some aren't.

  I am a very big myler bits fan - have been for years ever since I attended a clinic with them that completely solved the issues I had been having with my TB gelding, Tiny.  If your mare is leaning on your hands, it definitely means that she is having bit issues, but, the MB33 mouthpiece is for a very well trained, obediant horse that needs a lot of tongue relief.  If your mare is leaning on your hands that much, I would say that she needs a bit of tongue pressure still, to help her back off of the bit.  I would recommend either the MB43LP mouthpiece, or the MB36. 
  I have used all three of these mouthpieces on my horses.  My gelding Brandy rides in the 33, and the MB05, both of which take pressure completely away from the tongue, and work off of the bars and lips.  That's great for Brandy, as his former owner rode him in a too small, too thick single jointed snaffle, and was very rough on his mouth, and so he didn't like bit pressure at all before I got him his Mylers.  My Tiny rides in the MB43LP, and ahs ridden in the MB36, also.  I love the MB36 mouthpiece - the forward tilt ported barrel.  It allows for a good deal of tongue relief when the horse is relaxed and obedient, but has enough bite to school the horse when needed.  Every horse that I tried that mouthpiece on loved it.
  As for a kimberwicke cheek, I like them, and think they are very versatile cheeks, and look very elegant on a horse.  However, if you are showing, and need to conform to the show regs, you can get almost the same response and feel with a Myler dee ring cheek with the hooks, which add a bit of leverage to a snaffle bit.  You can show in them, and use the hooks, as long as you also use a curb chain.
  I can't recommend enough that you should get the Myler book, and read it.  It's a very informative read, and it goes through all of their mouthpieces, and what types of horses each would be good for.