
Definitely a harness :)
I have tried loads - some sit too close under the armpits and rub, so check the fit and also the stiffness of the webbing. You could always get a super made to measure leather harness if your frenchie has finished growing.
I use the soft Puppia harness for my boy - he was a consummate puller, but with the soft harness and a longer lead, he is now perfect! He also suffers from sore armpits at times and the harness doesn't rub at all.
You might think the soft harness is too frail for a frenchie, but my boy is very slightly over standard and is a real bulldozer, but this one is strong enough and works well for us - I bought him the black flame one from elmo's wardrobe. You can see him wearing it in my pics. I'm so impressed with it, I'm just about to buy the pink flame for our new little girl! :)
Three measurements are taken - neck girth, body girth and body belt - Pierre wears an XL
Before this, I used a figure of 8 'stop pulling' harness , the Lupi harness, on Louis - an excellent 'grow with your dog harness,very nice looking, not cumbersome at all and very kind on your dog's body, but it never worked until I realised that getting a longer lead was the thing that was needed. Maybe frenchies are a little too independent and inquisitive to want to walk to heel....or maybe it's just mine LOL
You'll also find that they walk quite differently when you use a fine 3-5 mm show set!