This is the one I have found to be both fairly effective in reducing pulling and pretty much escape proof. It’s a bit of a pain to put it on, but gets easier once you’ve practice a bit. I like that both the collar and the “harness” portions are relatively loose when the dog doesn’t pull, and when he does, it tightens around the chest instead of the neck. https://www.amazon.com/Harness-Lead-Comfortable-Resistant-Reduces/dp/B07ND5R4C5/ref=sr_1_28?

You will need to try it out to ensure you are comfortable with where and how much it tightens on your puppy, but it’s worked well on all the dogs I’ve used it on.

If you ever watch Pitbulls and Parollees, this is the harness they seem to be using on their dogs these days.

 

We used this one https://www.amazon.com/gp/product/B0719D4656/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

 

It's excellent. We use it, as well.

 

We’ve used the PetSafe EasyWalk harness with great success. It prevents pulling because it fastens to the leash at the chest, so any forward movement pulls the dog back toward you. We have graduated our 15 month old Golden to PetSafe’s 3-in-1 harness that lets you used it as a traditional harness (clipping at the back), a training harness (clipping in front), or a car seat restraint (comes with a lead that attaches to the seat belt). Highly recommended. I use an additional tether to our Golden's collar in case he slips the harness.

Easy Walk® Harness
3 in 1 Harness
https://www.amazon.com/dp/B07KM9GM7P?psc=1&ref=ppx_pop_dt_b_product_details

With regard to chafing, if the harness is fitted properly (snug but not tight), if shouldn't chafe.

With regard to the tantrums, I would suggest that is a separate (training) issue. Have you engaged a good trainer for Scooby? At 6 months, I would work on getting him trained so you don't have to deal with the tantrums into his adulthood.

 

How about something from ruffwear? They have a wide range of harnesses that are very very well made with many adjustment points.

 

Speaking of Ruffwear, I just ordered this one and have had it for about a week. I'm still trying to adjust the size, because he was right on the cusp, so I sized up. As soon as he gets a wee bit bigger, it will fit perfectly. https://smile.amazon.com/gp/product/B082FN9SSH/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

I also ordered and have not received yet a Lupine Roman Harness. I purchased a leash from them and LOVE it. Also love their Even if Chewed, Lifetime Guarantee!!

Reflective Roman Dog Harness

LupinePet reflective Roman dog harness is available to fit any dog, teacup to giant! Designed to eliminate pressure on the delicate throat area and prevents even the best escape artist from backing out. Safety, security and style in one. Guaranteed Even if Chewed.

www.lupinepet.com

 

I have noticed his hair is thinning at the armpits.

Harness for walking GRs... umm are you trying to make your GR into a sled dog? Since harness teaches dog to pull.

I do have harness for my 3 month old pup as well, but it is solely for car transport.
Kurgo Impact car harness, link: https://www.kurgo.com/harnesses/impact-dog-car-harness

When out in the walks, i use choke leash, that i can adjust freely how much of a choke it produces.
Hunter Freestyle Retriever, link: https://www.hunterpetstore.com/coll...og-leashes/products/adjustable-leash-freestyle-retriever?variant=39287172333602

During walks he is very active, and mostly behaves, except he can get bad tantrums when he does not get his way or is overexcited (jumping up, biting me, biting the leash, running around me in circles, trying to slip the harness), so that harness style has kept him from slipping it on more than one occasion since, try as he might, he cannot slip it. Because of his (sometimes severe) tantrums, I am not willing to get something like a gentle leader.

Your pup is in his early teens and tantrums are normal. However, harness doesn't teach him to calm down, instead, it may make it worse.
And as far as jumping up, biting etc goes, for that is obedience training.

 

We are working with a trainer on leash reactivity and as far as pulling on leash goes we use a Martingale (sp?) collar. Trainer advised not to pull on the leash if dog pulls. If there is tension in the leash from pulling he advised me to act like a "tree". Just don't move or speak. After doing this for a while(which admittedly is frustrating) the dog just stops pulling most of the time. We are working on that. He says not to use the leash to direct the dog. Says not like part of a car. Instead use your voice when you move or change direction..."come". So much we are learning. Can't list all. Commands should be issued 1x. I know everyone has their own take but I have had 3 GR's now and this is first I am learning some of this stuff.