Heya Soph, welcome!! I'm sorry I don't know anything about Brittany but I'm not long off the nursery slopes in terms of surfing so I know what it's like starting out

1. Definitely go for lessons - you will get the most out of surfing that way. You'll also stay safe, tides and rips can be death dealing if you don't know what your doing. A local instructor will put your safety in paramount importance at all times and teach you how to be safe too! I hope they have good instructors with a high level of English (and want to actually speak it!) You know the French!

2. You'll get tired

it's a fantastically vigorous sport and you'll be wrecked after a day or three so I'd advise breaking up your learning.
3. Only hire at a place that has lifeguards or where you KNOW the beach well, that means the tide, where the rips are, how the waves break at certain times of day etc. (See point 1)
4. Prepare to be addicted!

surfing is just about the best sport in the world and there's something about it that drives you to want to do it again and again and again!! It's flippin awesome!
5. You're in the best place to ask questions, read EVERYTHING on here (I did) and ask questions, start in the lessons section that gives great advice on how to do everything and what you're to expect. You'll be coming back here often

And have an awesome time!! Post up how you get on and share the stoke!

happy hunting.