Most ridgebacks are soft as anything.
BUT, check out the list of potential ailments in bj.any's monologue. They all cost money to treat, and the ridge itself is a mild form of spina bifida. Some are born without the ridge, but they are often strangled at birth by the breeder, so as not to pollute the breed. Nice, eh?
Ridgebacks are not alone. Most pedigree dogs have congenital defects particular to the breed, and that means discomfort for the dog, and a fortune at the Vet's for you.
To the OP, you're obviously approaching this with an open mind, so get down to the rescue centre and see what they have. They know the dogs in their care, and should be able to guide you with your selection.
Mongrels are also healthier. My last four have only ever had visits to the vet for regular jabs, and a grass seed in the paw.
Each of mine have had totally different personalities, which is one of the joys of dog ownership.