Excellent! With a car you will have many more options available to explore in and around the Pyrenees. I'd recommend you look to follow something along these line (driving south-east down from Saurat):
Saurat - start
Foix and its Chateaux
Vall de Aran - spend night
Vall de Boí
Aigüestortes National Park
La Cerdanya
Puigcerdà - spend night
Vall de Núria
Queralbs
Ripoll
Rupit - spend night
Besalú
Anchient Greek city of Empúries (Emporion)
Cadaqués
Collioure - spend night end
(Continue to Provence)
These above recommendations follow a logical geographic flow, starting in the heart of the Pyrenees and ending on the turquoise Mediterranean coast. Note if you will be traveling in the Pyrenees in December, you may encounter some extra delays/issues due to the potential for heavy snowfall and subsequent road closures. Hope this helps :)