Sounds like your horse's pain needs to be addressed at the source. Another piece of equipment is not going to make the pain go away, and as AlexS stated, the "martingale should have zero effect..."
You need to address the pain, maybe then you will get the collection you are looking for. Head carriage should be natural and not forced, however it can be taught with collection excersices. No matter what the head carriage might be, it doesn't FIX the pain.
One is closer to God's heart on a horse than anywhere else on earth!