I suggest snaffles. While they’re considered mild, all bits can apply more or less pressure according to the hand behind the bit. Another thing to keep in mind: the thinner the mouthpiece, the stronger the pressure will be. I hope this helps.
Yeah try the grackle with a normal snaffle first and then see I would then ask your trainer what they think about a Dutch gag or kimblewick that has been the golden combo for my ponies jumping at home
I would not straight away go for a hackamore as your horse might not be the best, does he list his head and consistently pull does he put his head down and rush after? What I’m trying to get at is what is he like when riding as someone could recommend a Tom Thumb when you might need a hanging cheek bit.