There are quite a few surf schools/ board hire places I don’t know the better ones but google surf schools santander, san sebastián,
You could also try having a blast body boarding in the patrolled swimming areas where you could be doing it together.
BY your request I am assuming you don’t have lot of surf experience so the school idea for board riding is probably the better idea, as the patrolled area body body leaves you both more to your own resources.
Under no account try surfing of either type on unpatrolled beaches or out side a school, -
Just pick safe and fun , have a blast

I've taken up troll hunting just for fun, instead of a rifle I'll just use a pun! 冲浪爷爷