I don't know if you have found a driver yet, but the best prices I have found are with South Ole Spain Tours. You could Google them and send an email to inquire. While their web site shows mostly group tours, they will also provide private transports.
If you use them before early next year, please please let me know if you were pleased. I checked for reviews, and on Trip Advisor they only have excellent reviews (but only a total of 21-22 reviews, so I think they MIGHT be a relatively new company). But, Emily who runs the company has been extremely prompt in answering my emails and offering to help with any other aspect of our vacation.
And we well understand the desire to not rent a car and drive.....no reason to add stress to what is supposed to be a pleasant trip. And, my sister has friends who experienced a flat tire in a rental car about 15 minutes after leaving Barcelona.....turns out it was a set-up and they got robbed on the side of the road by two guys who had presented themselves as offering to help the couple in need. They were left on the side of the road with the flat tire, no passports, no money, no credit cards, no cell phone, etc., and they didn't speak much Spanish. Not a good way to start the trip.