Hi Maria,
You can find a summary of the Chemin d'Arles
here. From Somport onwards it becomes the
Aragones.
I have just walked the Arles route to Castres, and the Gronze site was very up-to-date with information. You really don't need more than their maps and accommodation list. I had planned to walk further to Toulouse, but it was too hot (this was during the 45 degree heatwave last month, think it's a bit better now! *edit - although I see they're anticipating temperatures of 40 degrees in Toulouse next week, yikes!*) Also, I was finding services on the Arles very sparse - one often has to walk 20km to get to the next water point, not to mention access to pilgrim accommodation or groceries. I think there are still quite long distances between accommodation after Castres, and the walk into Toulouse is along the Canal du Midi, which I've heard can be very tedious (the canal snakes up and down across the landscape, so progress takes ages). Things might get better after Toulouse, I have no idea - best check Gronze for info. The site is in Spanish but you can get lots of information about stages, accommodation, maps, profiles, etc. Easy enough to translate the detailed "recorrido" with Google. Also, there are lots of photos for each stage, so you can get an idea of what the landscape might be like!
p.s. I've also walked from Oloron-Sainte-Marie over the Pyrenees, and really loved it. I don't remember it being particularly difficult, but it's obviously different if you've got an injury...