Jacket extensions are an excellent option to adjust the jacket size to an intermediate between two regular sizes, by adding a few extra inches to the jacket.
If you do not find the back extension that you are looking for, simply design it yourself and build your own customized solution.
Large Animal, Custom Jacket Back Extension
Made of spandex / nylon fabric -spandex provides elasticity and maximum comfort for the animal, by helping the garment follow the animal's natural shape.
Jacket compatible zipper - facilitates insertion and removal from the jacket.
Full Length: the distance from base of the skull to the junction of the tail and body.
3/4 Length: 3/4 the distance from base of the skull to the junction of the tail and body.