"I've even helped design the logo and website of my mum's freelance business. That's how i realised it's not just creating the art, but marketing and specifying for a client that i found i loved"
Have you considered graphic design instead of art if it is an option? I studied it at A-level and this is the sort of work you can do for a project as well as illustration if it fits, so you may enjoy it.
If you can, try to find out how the art subjects are taught at the college to see if you would enjoy them; avoid them if you think you will burn out again and/or won't enjoy the course content. This especially since you are already enjoying your subjects now and you don't need art A-level to study it at university—only your portfolio (there could be rare exceptions). I don't think switching to English would be necessary as they aren't looking for specific a-levels, is this for a lower workload perhaps?
The art foundation year others have mentioned is a good idea if you are unsure if you want to pursue an art degree or fall short of entry requirements. If you study at a university, you will almost always be guaranteed a place on related art courses there if you pass. Look into if you can study locally though, as there is no maintenance loan to cover living expenses if no university or college offers it where you are. It will be free if you leave college at eighteen (it's a level 3 course), or £5421 otherwise (there are other learner loans through student finance you can find but this option may be inaccessible if you are unlucky).
You could still study one of the “safer” degrees at university but pursue illustration during or after your studies and use the degree for a backup career, or use your degree and have illustration be a side-job. You evidently have the passion that would be a shame to waste if you never tried to pursue the career as you desire, whether through university or not. The mindset about feeling like you need to get a job with money is a factor in why we unfortunately see low representation of working-class people in creative sectors. I would say to have a solid plan if you decide not to study illustration to minimise regrets and maximise the value of the degree you do choose, rather than trying to figure it out later and finding the degree not being as useful as you hoped.
I don't have graduate wisdom so take my advice with a grain of salt. Good luck.