Hi! I do English lit, History, Politics and French (AQA) and i'm starting yr13 in september. I also found GCSE French easy to the point where I made a bet with my friends not to revise in order to test my 'raw French ability' in the exam and I went into yr 12 picking it because I didn't really know what else to do and I knew that I liked languages in general. I genuinely gained a passion for French this past year and doing it in sixth form made me realise I wanted to do it at uni so I'm applying for French & Linguistics!
I would say, if you like languages and you find it fairly easy at GCSE, give it a shot! It is quite different from GCSE in the sense that you learn about actual culture, politics and history, not just random floating topics. It's like you put all the random bits and bobs you learn at GCSE into real world context and that's what makes it so fun because you get to debate real issues. The focus is less on you and your life (such as your family, fav sport, fav subject etc) and more about topics like tourism, diversity, music in a wider sense, french cinema, etc, however nothing you learn at GCSE is wasted. My school taught us A LOT of grammar at GCSE and I found that at a-level, it wasn't really anything too new. It's either just developing a grammar point or brushing up on old points, but since my school covered everything from subjunctive to object pronouns to the pluperfect, it wasn't much of a struggle.
You use a lot of what you've learnt before like grammar and vocab, so a-level is just about developing your analytical voice and being able to confidently explore contemporary francophone issues and areas of interest. You also get to study a book and a film (which I loved as I also do english, so analysing them is so fun) and the a-level gives a much more holistic view of french studies in multiple areas that you don't get at GCSE because it has to be quite general. If you're also interested in politics, we look at french politics and it's so interesting (especially with the recent elections that took place in france and now the olympics). What made it so easy for me to enjoy French was definitely my passion, because if you can't truly be bothered, it won't be enjoyable.
Sorry for the PARAGRAPHS, but if you have any questions, feel free to ask, regarding French or any of your other two subjects as I also do them. I do both OCR English lit and OCR History btw.
P.S: If the school you want to go to has their curriculum/ scheme of work which tells you what you learn in the a-level, you can have a look at it and do some research around the topic by looking at revision materials to see if it interests you or not. Good luck!