Hey, I was in pretty much the same situation as you - however I have just completed the whole qualification for marking this summer. I study French and Spanish and English Lit and History - hoping to study French and Spanish at Ox too.
I chose to study the changing role of women over the years surrounding the spanish civil war. it sort of evolved as i went along, taking in elements from all my as-level courses and it allowed me to study in detail two poems and a novel, and a lot of historical context.
I would recommend choosing either french or spanish - at the start i desperately tried to find some way of comparing the two but i couldn't in the space and time, 5000 words is not a lot. Are you doing the project over the summer holidays? If so, think about places such as museums or libraries (or perhaps take a holiday in france/spain?) that are local or accessible - as this is sure to strengthen your project and application for it. I didn't get the chance to do half as much stuff as I would have liked, because I was doing it alongside my other subjects and an exta gcse on the side, including extra curriculars and so i think it would be better to have an extended period of time to concentrate and immerse yourself in it.
What did you study in English lit this year? We did the war literature stuff, and so I was sort of inspired by this in choosing mine.
Sorry if i haven't been that helpful
xx