Hi,
I had an old style Halti with horizontal chest strap for Salty, but that made him walk funny
So I got a Perfect Fit and its absolutely excellent
If you can go somewhere and get a fitting then best as I used the online fitting instructions and although its nearly correct I had to reorder a smaller front piece (which is a free swap)
I used the original UK site:
https://www.dog-games-shop.co.uk/perfect-fit-fleece-dog-harness.htmland I also found this:
https://peterdobias.com/products/perfect-fit-harness-builderSalty is 12 kg, Girth 57 cm neck 33 cm, he is 1 year 3 months old, and pretty lithe and athletic
I ordered the 20mm S-S-M (consisting of a Size S Top piece, a Size S Front piece, and a Size M Girth piece) Perfect Fit Harness (53-63cm)
The top and front pieces are adjusted to the smallest adjustment, the girth let out around 1/3, and its a great fit, except that I should have had the XS front piece since its a bit too loose around the neck. I have an XS front piece coming, and will update how it is when it arrives
Given how hard Salty can pull - I wouldn't go for the 15 mm wide sizes.
Salty really likes to put it on, which is amazing for him and tells me he finds it comfy
Salty is as mad as a box of frogs and pulls like a steam train, but with a double ended lead (actually from Halti - which is excellent) he walks to heel although still with a lot of steering and perseverance.
When we are jogging I have the Halti lead round my waist and the other end only onto the PF harness back ring and in the beginning he pulls me along at MACH 3 but he is still comfy (although with the new smaller front piece it should be even better) and I am getting fitter
Although I go early and don't go to far (I say that's for Salty's sake , but also since I am no Olympian) , it can be warm here and there is no overheating due to fleece as its low area, dogs don't loose heat like us sweaty humans and I have felt under the fleece straps immediately after jogging and it was not at all hot there
In summary, I would advise a Perfect Fit with a Halti large double-ended lead - based on my own limited experience of course
Abraços from Portugal