My Fletcher was pretty big, around 90 lbs (40 kg) and very leash reactive to other dogs, so I understand what you are dealing with. He pulled me off my feet many times, but luckily never broke anything. As you have discovered , the harness gives much better control than a collar and the Ruffwear ones mention above are good, but no harness is going to help you control his head. A wide (2") cloth collar will help you control his head/neck with much less chance of injuring his neck or spine. A leash attached to the collar and another leash attached to the harness will give you the most control. If you haven't already, trying the "look at me" training is worth a try, it can be very effective. Unfortunately, it didn't work for Fletcher, so it may not help your boy, but worth a try. The only other thing I can add is I learned to be hyper vigilant on our walks looking for other dogs. If I spotted the other dog before he did I had much better control. The times I got pulled off my feet and he almost got to the other dog is when I didn't see them coming. Good luck!