Searching for the right bit!

So I ride this horse, his name is Pie. He's a 14.3hh something. Right now we ride him in a happy mouth shaped mullen kimberwick.

Happy Mouth Shaped Mullen Kimberwick - Kimberwickes from SmartPak Equine

My problem is, is that I don't believe this is the right bit for him. He bends a lot at the poll and doesn't respond well to the bit, as in he doesn't really have good brakes. He doesn't act mean or anything, a perfect gentleman when putting on the bit, but still he doesn't respond well or at all.

I personally think instead of bitting him up we should go to to a softer bit. I talked with my trainer about this and she said she thought it was a good idea and said maybe a slow twist or a double twisted wire.

I am open to hearing what people think, so if you think bitting him up may be a good idea I am all ears, but I am hoping to get some others insight on just what type of bit may be good for him.

Thanks!!

Your trainer knows your horse better than you can explain your horse to us. Still, IMHO, your horse needs to be trained to "Whoa." THIS is a serious problem and stronger or milder bits won't fix it.
If you get a chance to watch any of the tv trainers who dabble in the "Mustang Challenges", you will see that they train a good "whoa" in one session on a green-as-grass horse. Your horse doesn't believe that he HAS to stop. You need to teach him "whoa" EVERY TIME YOU LEAD HIM. I have done this with my DH's horse--the big head, left. I am 5'4" tall. His horse is 16'3hh, which means his withers are 5'6", therefore, 2 inches higher than I am tall, a BIG, >1,400 lb. Animal. He gets stalled at night during the winter and I lead him to turnout. I was determined that this horse would NOT run over me...EVER. So, whenever I lead him ANYWHERE, we halt, back, "walk on", "around"--I have taught him the English and I cue with my body and the lead. Even when it's icy and he's been inside his stall for a week, he never rushes and runs over me on the way out. He is getting so good at this that I am anxious to show him off bc it reminds me of what I see on some of Clinton Anderson's programs where the trainer and horse move together. It didn't take me a lot of skill, just daily work.
Teach your horse excellent leading manners, teach "whoa" when you lead, then you can translate that to under saddle. It becomes a habit.
BTW, the slow twist and double twisted wire bits are more severe. Did you mean to say that your trainer disagrees with you?

I didn't read much of this, so excuse me if you already said something about this.

But as a general rule, I do not think that a bit will fix any of your problems. Work on his training, rather than his equipment.

Plus, this horse is not yours and since he is simply a schooling horse, you don't (and shouldn't) have a say on what bit he wears or doesn't wear.

Best of luck!

I am leasing him, so I kind of do...but not really. And I didn't know that a slow twist was a harsher bit than what he had. But, I will be working on his training (thank you for that advice, as stupid as it sounds I hadn't even thought of it) and also I think he may benifit from a change of equiptment because of how he bends at the crestish part of his neck (what I am trying to say is he looks like a giraff) and my trainer said that the bit he has can cause that....? either way thanks for the advice.

A lot of horses are not going to respond to an extremely soft bit. Maybe they would if they were just starting out; but you are usually working with horses that have been ridden by different people with different riding styles. If the horse won't stop, a softer bit is unlikely to help.