From what I have been taught, there is no set structure for any form of literature essay. You can have an introduction, a conclusion, both, or neither.
An introduction although I find is key to setting up your essay. That's where I'd include all the nitty gritty details, like the period in which the text was published, the theory you're writing about, your stance etc. Anyway, you know the drill with introductions I assume.
However, for the body paragraphs, I find it is easiest to work chronologically, specifically focusing on each scene rather than on specific themes, like agency and voice etc. I find that if you work by theme, the essay can become messy as these ideas are so embedded throughout the text. So, you find a scene that supports the ideology behind your theory, like feminism, analyse the scene and work the theory into your response.
I.e. "Conrad layers on animalistic and primordial behaviours & characteristics, according to Achebe, to separate European’s “vaunted intelligence” from their lingering ‘threat’; “[the] suspicion of [the Congolese] not being inhuman”. This suppression of humanity is evident when Marlow states that the “few months of training had done for that really fine chap”, resulting in the fireman becoming an “improved specimen”, reinforcing western ideals of assimilation and consequent civilisation. "
"Marlow abides by the rigid patriarchal ideology, describing his Aunt with tender adjectives, like “excellent” and “triumphant”, perpetuating the ‘women-are-wonderful’ effect. This effect acts under the guise of nurturing and sympathetic qualities, but unveils Marlow’s, and thus Conrad’s, male chauvinist views".
So, I suggest to work your paragraphs scene by scene, aim for at least 2-3 decently sized body paragraphs and remember your vocab!
Anyway, I probably butchered this. Best of luck.