Don't get a gentle leader! Ask two dog trainers for advice and you wil get tow different answers!!
You have to teach the dog the correct position not just punish it for being in the wrong place.
So get a clicker and get the dog used to the clicker . Click the clicker and give a treat do this for several days until the dog realises that the click means yummy treats. A lab puppy will take about 3 mins to work out what is going on.
Then lure the dog to your side where you want him to be walking and click and treat. Do this in the garden without lead on. When the dog goes ahead gently lure him back to the right place and click and treat. Then holding treat in your hand walk forward a few steps and click and treat the dog if he is in the right position. When he is happy in the position you can start to add a word I have close for my left side and side for my right but up to you what you say.
Then put on the lead and off you go! (If only!) He will pull ahead the second the lead goes tight stop, do not say anything at all but the second he turns his head towards you click and treat and lure him back to your side and take a few steps forward with a lose lead, again the second the lead goes tight just stand still.
Be prepared to be very very patience here. It may take him ages to turn slightly towards you just wait it out he will eventually! It will take a while to get started and you will get fed up and you will think it is not working but trust me I am dog trainer! It will work. A few week now of getting this sorted means that the next 14 years will be pull free and you will be able to take your dog anywhere
Do not get into the habit of letting the lead go tight and you pulling him back. This will just create a circle of pulling and pushing. The dog has to feel the tight lead and then the dog has to make the decision as to what will alter that tight lead. The more times he gets a tight lead to start with the more opportunity he gets to learn the correct behaviour so do not panic if it takes time.
Joking apart about gentle leaders if you do need a head collar go ahead but my grip with them is that the dog never learns how to walk properly and is just restrained from pulling. Also a determined dog will pull even with a head collar and this can damage their necks. But it is a personal choice