ManMat RUN Long X-back type harness which has been used but is in great condition, although washing hasn't totally managed to get rid of all hair from the inside - but no smell or damage!  Bought new for £38.95.

Although designed for active/sports dog activities, we actually used on our Staffy X to long line train, so that the lead was attached to the cord at the back and didn't go under her body and legs so easily - avoiding lead burn when she ignored us and we had to pull her back!!

She has outgrown this (and also the size XS that I am selling separately) but they were great - only thing to be wary of is that there is no clasp to undo the harness - you just have to fit it over their head and get their legs through it so not super easy to get on.  But if you are determined to train well, we thought this really helped!

This is size XS - from ManMat website: -
SIZEA - GIRTH NECKC - BACK LENGTH (approximate)DOG WEIGHT(approximate)DOG BREED (approximate)
XS39 - 42 cm54 - 56 cm14 - 16 kgborder collie (female), australian shepherd (female), samoyed (female)
S43 - 46 cm57 - 64 cm17 - 21 kgborder collie (male), australian shepherd (male), samoyed (female), siberian husky (female)
M47 - 50 cm65 - 69 cm21 - 25 kgbelgian shepherd (female), german shepherd (female), labrador retriever (female), siberian husky
The inside padding allows free movement during various activities in every weather.

The harness is made mainly for sports where the dog pulls since it helps spread out the pull force.

The reflective components are sewed on the sides and on the cross and they allow good visibility of the dog while not having blinding light.

NOT suitable for weight pulling!