I don’t recommend harnesses for leash walking
1. Your dog being a bit uncomfortable when pulling on leash is not necessarily a bad thing.
2. If you’re struggling with control and leash walking already, a harness is the last tool I will be recommending for most dogs.
Here’s why.
With a back clip harness you have very little control. If your dog pulls or reacts, they have the most comfortable means to keep pulling harder. And you have the least leverage of their front end to safely steer them away from anything they may be reacting at. Difficult with a small dog. Increasing your chance of a serious injury with a larger dog who is prone to pulling already.
With a front clip harness, constant pressure without training lands us with much the same issues as a collar being constantly pulled on. The pressure from the front of the harness being pulled across or the restriction in movement from the tight around the legs style frequently leads to gait issues when used without training in place.
For most pet dogs, a collar and leash is going to be the tool I recommend for your leash walking. It allows for clear pressure and release - teaching them that if they feel tension on the leash they should move back into position to release that. And it allows us easier turning to redirect dogs with less force required, which is especially important when dealing with powerful & reactive dogs.
Harnesses may be appropriate for dogs with specific health issues. They can be great for young pups to explore the world in when not working on your leash walking skills, so that you don’t practice them being allowed to pull in a collar while working on other goals. They can be great for activities such as hiking or walking with a well trained dog, for tracking or other sport work (eg in agitation work where we want the dogs pulling against the harness and building drive towards the decoy). In these instances I recommend a well fitted Y-shaped harness which allows for full range of motion of the shoulders to reduce gait issues.
But if you’re already struggling with control and safety with your existing dog on a collar and leash, a harness is likely to add to your problems - not solve them.