The Corgi spine has the same amount of vertebrae and the same spacing as for any other dog; their weird proportions are due to their legs being so short and not their spines being any longer. As a group, the Welsh Corgis have been called "yard long dogs" for ages. And, unfortunately for Corgis and other chondrodystrophic breeds, their risk of
intervertebral disc disease comes with the genes, not the conformation and not the lifestyle. You could get a Dachshund and do all kinds of back-strengthening exercises, make sure the dog never jumps, do hydrotherapy, etc. and the dog will still blow a disc because it's pre-determined by genetics. A dog who does nothing but sit on a pillow and do prescribed gentle exercises may still have IVDD due to the genes causing chondrodystrophy. A good article written for the Dachshund Club is
here.
The other danger with backs in Corgis is
degenerative myelopathy. Recent testing of Pembroke (no-tail) Corgis show the "clear/unaffected" percentage is 9%! Boxer dogs and other breeds are affected, and this has a genetic basis and is not limited to dwarf breeds. Thankfully, there is now a
genetic test for this. Since my dog is a mixed breed, and the gene is recessive, I haven't done it but I would if I had a pedigreed Corgi.
I've looked a bit into Corgi stuff because my own dog is chondrodystrophic/dysplastic. I debated whether or not he should roughhouse at the dog park, and in the end I decided to let him live his life, not least because his discs are already degenerating, if that's their fate, but also because I'd rather he live a full life than a life in a bored little bubble. If we hiked all the time and he was used to it, and strong, I wouldn't worry about a little backpack. You can get vests with a pouch, though, if poo is all your concerned about carrying. You can also use something like
this or
this (but don't use a retractable leash!).