Well in general harnesses promote pulling. That's what they were developed for, to help a dog pull. Look at the dogs you see wearing harnesses... sled dogs, weight pull dogs....etc. Harnesses also make it easier for a dog to pull as they can get all their weight into it, use their whole body so to speak.

What I would do is put him on a properly fitted flat buckle collar and a leash that's at least 6' long. Take him out and get him to sit. Give him a command (I wouldn't use a formal command like heel, but an informal one like "let's go") and start walking. When he goes to dart past you abruptly turn around and walk in the other direction. Don't say anything until he catches up to you. Praise him when he is at the right position. If he goes to dart past you again, just reverse your direction again. Do this as many times as it takes. You may look a little silly walking up and down the street, but if that's what it takes....

What this does is teaches your dog to pay attention to you. You are unpredictable and so he has to keep a close eye on you to see what way you are going to go. If you are worried about him hitting the end of the leash too hard, give him a little warning like "uh-uh this way" as you are changing direction. Don't wait until he is at the end of the leash before you turn. You want to give him the room to realize he's made a mistake before he hits the end. Always praise him when he catches back up to where he was supposed to be, maybe even give him a treat or two to reinforce that your side is the best place for him.

Good luck!!