Hi, I think you got some great advice! Don't be afraid to increase pressure until you get the desired response. The release is everything, though - make sure to reward the slightest try (horses learn from the release, not application, of pressure). So no matter how much pressure you apply, if you release as soon as your horse BEGINS to do the right thing (there's such thing as a partial release - lighten the pressure when he THINKS or BEGINS to do what you want, then release it completely when you've got the complete result you want), you'll get a light, reactive horse.
Sometimes, however, as you increase the pressure, the horse will like you said, throw his head up, or do things that will intimidate you. To deal with this, I would teach your horse the one-rein-stop from the stand still. Then when he starts trying to intimidate you and you feel like you can't ride through it, you can turn your horse's head and ask him to yield his hindquarters to create energy that you can then later turn into forward energy. With your horse's head turned, he's in no position to intimidate you...as long as he already knows he has to give. If he won't yield his hindquarters when you're on, try it on the ground first, so he knows what you're asking him (in fact, I recommend trying it from the ground first)...I started a little morab mare last year who refused to walk forward when I was on. This is how I taught her, by creating sideways energy and re-directing it later. Every time she stopped, I had her yield her hindquarters in a circle, which is harder than walking straight. Now, I have to work on slowing her down!
Here's a little training vid my brother and I put together. It's for misbehaving horses, not ones that won't move, but at least you can visualize the exercise:
Please let me know if this helps/if you want any more advice!! :)