my understanding is that 'I' is fine, and you will read plenty of academic writing that does use I. Just don't follow it with an anecdote about a conversation you had last week with a cashier at Woolworths, you know? Using I doesn't make your writing informal, writing informally makes your writing informal.
This is a bit from a mod A essay that I specifically asked my teacher about and which she said was totally fine
...Hymne to God, in my reading of Donne’s later religious poetry, is an outlier. Its tone contrasts markedly with the pugnacious 2nd person addresses of Donne’s holy sonnets (“why swell'st thou then?”etc.), in that it is singularly introspective...
I even think this can be good, as
(a) it will set you apart from other students, and your absolute priority in advanced (I think) should be to set yourself apart. Because markers are bored shitless.
(b) it gives you a bit more credit for your original ideas. It's like a little signpost that says "I did not get this from sparknotes, or from an academic reading", which, even if subconsciously, should make your ideas a little more impressive. I think.
Having said that, another of my English teachers is always saying that the idea "it is raining outside" is not enhanced or expanded by adding "I think it is raining outside", so do not slip into tentativity when you start writing in 1st person!!
Hope this helps and good luck!!
