I completely understand, OP. Last year I did an online shop in advance (Carrefour) that we collected just after we'd got to the house. Massive amount of food, as we were four adults and four kids, for two weeks. I was really proud of myself! We ate most of it in about 4 days 😁
I also did a meal plan but this was really more of a list of easy main dishes with a mixture of side dishes - stuff like roast chicken with green salad, coleslaw and bread; tomato tarts with pasta salad; a boatload of cheese, charcuterie, grapes, apples etc.
Lunch for us is pretty much always picnics on the beach, and prepping that gets boring - I don't think there's any way round it really, unless you want to eat at cafes every day!
(One good thing about French supermarkets is they often have a traiteur section with, essentially, nice ready meals. I'd make the most of the same thing in the UK if poss, at farm shops.)
Also: It's a bit dickish to the OP's proposed holiday sounds depressing, or that she should go AI indtead, frankly.