Just use the French mail. We found their services exceptional and cheap. Many post offices have packing boxes. We sent several packages of excess gear to SJPDP and paid no more than 12 or 13 euros a time.
We have just started blogging on the Le Puy route. We are new at this, but hopefully it will improve over time.
https://ritvaandpeterschemin.wordpress.com
This site is run by Ivar at in Santiago de Compostela.
This site participates in the Amazon Affiliate program, designed to provide a means for Ivar to earn fees by linking to Amazon