It does sound like he still has some puppy fur. We just got the last of it out of Sophie and Syrus about a month ago. They are 14months now.
I have spent muko
bucks on various brushes and combs. I think you will find as many answers to your question as there are products to use.
I have the following: Mars King Coat - long toothed pin rake - Furminator - professional groomers comb - and three slicker brushes, hard, medium and soft.
I like the medium slicker brush the best and surprise of surprises, it is the cheapest. I have used this since we got them and it works great for getting out yard twigs, stickers and prickers and keeps hair from matting. It also gets out the shedding. The bubs tolerate this brush as well. Not the 'hard' however. The Mars King seemed to cut patches out, the long toothed gets too snarled and bubs get impatient. Forget the comb unless he is really clean and you have hours of time. And they just don't like the Furminator, they act like it hurts.
I get them professionally groomed occasionally when I want them trimmed up and she always compliments me on what good shape they are in. She has two other clients who have Newfs and she usually has to shave them down to get the matting out.
You will probably need to do a little trial and error to find what works best for you and Luke. I'd start with the cheapest.