Whilst I'm usually super pro-bitless (or at least pro- people trying it) I'd be cautious in this instance - do you know how your horse would go in a gentle bit (something like a french link, a straight bar rubber bit or whatever bit you usually use) with no nose band? There may well be bitless options that suit this injury well, just nothign that I've used immediately springs to mind.
His fractures are in his cheek below his eye and at the jaw joint above his eye. I've already tried him in the miklem multi with a snaffle and he seemed uncomfortable (rubbing his mouth on his leg) and going forward but with pinned ears. I am not using any contact so as not to give pressure. He is doing well on the lunge however. The vet has said ok to ride gently with a bit.
Depending on the exact location of the fracture the Miklem might actually be pressing on the section below his eye? The throat lash section comes off the bridle at that point whereas on a conventional bridle the throat lash comes off higher. I would try a normal bridle - with or without noseband - loosely fastened and see if that makes a difference. Like Girlfirday I'm pro bitless too - but anything that puts pressure on your horse's face is likely to be uncomfortable for him at the moment.
I would use a simple sidepull if possible, the micklem crosses under so will have a squeezing action which I would think is definitely not desirable with a fracture.
No - a hackamore puts pressure on the nose and poll. A side pull only puts pressure on the opposite side of the face - unlike a cross under (which the Miklem is) which squeezes the nose. A sidepull really works much like a headcollar - you want the horse to go in a certain direction you point his nose at it by pulling (hence the name) on that side. There is no refinement in the bridle - all the subtely comes from the rider's seat and body. They are lovely bridles - everything comes from the rider. But both you and the horse need the experience in riding from weight aids alone. Its a discipline worth mastering - but possibly not for the first time when your horse is recovering and likely to be fresh!
Agree with Shay - love sidepulls and they would probably be fine now I realise how high the fracture is.
But, also agree that when horse likely to be fresh/unpredictable if his injuries have a sudden twinge of pain isn't necessarily the best time to try.
If you've previously ridden in a (well-fitting) head collar that is not dissimilar and may be worth a shot in an enclosed arena. Or you can get quite cheap synthetic side pulls (endurance people use them over many, many miles of open country - they can be perfectly safe, and washable!) to try if you are confident in your horse but not sure if the bridle will suit.