i know this probably isnt all that useful since i cant rlly say exactly whats right for you, but if you like or care about english, pinpoint or find something exciting to you, something maybe that was very briefly touched on once in class but never brought up again. or maybe when doing your own reading, struck you as an interesting train of thought. or an argument that appeals to you whenever you read that never seems touched on in class. if there is anything like that then start googling, key words, note down any branches of literary theory, essays, or secondary texts that even vaguely relate. save links. even if you end up dropping it it could still be interesting.
honestly, virtually anything 'works'. if that is something that interests you, start looking into it! you really can do it on anything you like. if youre interested in pursuing english then the mere fact that youve taken time to read essays, academic texts, plan, write an extended piece, etc, does look very good as far as im aware. it makes sense! if its on something highbrow literature-y then that obviously makes it sound even better, but the most important thing is that youre interested in the subject because if you arent then itll be harder to find motivation.
as for choosing a question, people i know took very different approaches. i wanted to study english lit at the time, and wasnt very comfortable with the close study of any text in particular, so went down a sort of literary theory/philosophy pathway - who owns the text, death of the author and such. this was good because it wasnt something we'd touched on but if you nose around for academic essays, resources are everywhere. im afraid i cant actually remember where i got that idea from though. maybe just my mind wandering in class. but any time you do start to wonder about anything thats just outside of the syllabus, write it down for future ref. make a spider diagram of all your musings, even if they seem random or far from what you wanna go on to study. like i said, the actual project itself is an impressive feat, so even if its a little off topic but you feel more comfortable with the area and feel like you have enough resources and interest to see it through, id give it a shot.
another girl i knew wanted to do english and she took a more specific approach, as you seem to be thinking about. she chose a specific text and theme and then compared it with other texts... something along the lines of, how does the exploration of 'X theme' in 'Y text' compare to other literary representations through history, or something? or how did it effect later texts, or how did it come to be in the first place?
so yeah if youve got a text in mind, jot down all the stuff you find interesting or exciting about it, and maybe structure it sort of like that? if you can get a teachers assistance fine-tuning the question that can always be good although i dont know the time scale of how your school does it. spider diagram, look up pdfs or other related essays, etc. see what you can work with. i think there is a possible epq in practically any topic, you just need access to the right resources, and to care about it to some extent.
another thing you can do is look at essay competition questions even if you arent planning on entering. there are lots set up by unis especially aimed at yr 12 students and so are aimed to not relate to any syllabus. check out past questions from the thomas campion essay contest, if not to use the questions themselves, see how a question could be formatted or just get a feel for whats expected at higher levels of literary study.
honestly i do think it was worth it although i cant say whether it harmed my other grades in the long run. maybe it did, i spent a lot of time on it. but not by too much. if you get it sorted out pretty early then it can be totally in the way and you can have a clear head when approaching actual exam study period (though like i said, i dunno the time scale youre working with) . i know plenty of people who dropped out because it was too much, and in my school that was fine. i know people who started it enough to put it on their personal statement, then dropped out when they got offers. i know a girl who did this for her oxford application. shes there now studying english. i think her EPQ was gonna be about the cello or something. point is she never did it, and theres nothing oxford could do about it once theyd given her her offer haha
(although SOME unis do now put EPQ on grade requirements, generally in exchange for a lowered grade i.e. AAA, or AAB + A in EPQ, although this seems fairly rare still?)
either way, its always gonna sound good. its kind of exactly what unis probably want english applicants to be doing since it is like a mini dissertation. so if you think you can, id say have a think and go for it! i also think it was probably helpful to me in some ways because learning stuff that you wanna learn about off the curriculum is really cool, and then if you bring anything new that no one else knows into the exams with you, then thats cool too, makes your exam papers more unique. i.e. you may end up writing about a school of literary theory that never gets touched on in class, and you might be able to apply it to your exam texts, which as long as you do it right, will help you stand out from the others who use the same old marxist/feminist etc. readings.