usually, no problem to get a pilgrim bed, the people from the pilgrim office(39 rue de la citadelle) will take care of you(on wednesday 9th I'll be there)ask for philippe. But if you want a hotel, you have to book before your arrival.
At what time do you expect to arrive in SJPP ?
9 trains from Bayonne to SJPP that day 8h58 to 21h11
maybe see you next week
philippe33