How to ensure your harness fits properly

Here's some more information:

I think the conclusions are still a little fluffy, but basically, a restrictive harness (one that has a horizontal chest strap) is bad for the dog. Also, anything that changes the dog's gait for any other reason - the Dog Games fleece harness (non-restrictive) was equally as bad as the Julius K-9 harness (restrictive). The advice is to choose a harness that has less contact with the dog's body (less surface area) and that doesn't have the horizontal chest strap.

The missing link in the research for me is how much the fit of the harness affects the dog's gait; the DG one doesn't have the same range of adjustment as the Perfect Fit, for example - how would that compare?

But, still, it is clear that horizontal chest straps are bad for dogs and it's likely that the more lightweight the better. So Balance, Haqihana etc are likely the way to go :)