Maybe try a figure eight for different leverage.
If your looking for a stronger bridle than a flash I think "double bridle" (normal English noseband + hannoverian noseband) would be worth a try, I've found it very good with horses that need something more than a regular flash but not a stronger bit :)
No a grackle is fine as long as your horse works well with it. Also I recommend trying a Waterford (bobble) but they work wonders!!