I usually point my clients to
handicappedpets.com. I find they have a very complete selection of aids.
The chest slings don't work for Degenerative myelopathy patients. With males, it's particularly important to have a sling that that keeps the belly open so they can urinate. My preference is to get one with rear leg rings. This worked real well for our Buddy (severe hip arthritis and ACL in one knee) but required 2 people - one to lead and one to support the back end. For a dog a little less head strong, one person could probably do fine.
I've had a hand full of DM patients in my career, a most difficult situation as there used to be nothing we could do. My brother's dog, Jasmine, died several years ago due to this disease, I felt pretty useless. At least now there is some potential with the stem cell therapy, not cheap and not fully proven, but very good first reports.
Doug, DVM