I am trying to come up with a good thesis and introduction for a two-page essay but I'm struggling. I want to describe this poem as an illustration or comparison of autumn to a woman.

"To Autumn," composed in September 1819 and published in a collection of Keats's poetry in 1820, is one of the last poems that John Keats ever wrote. Many poets and critics consider it one of the greatest English-language poems ever written.
As for your proposed theme of "this poem as an illustration or comparison of autumn to a woman," it may not work exactly as planned. There is no indication that Keats intended to compare autumn to a woman. However, the poem is full of personification, and it might be better to adapt your theme to Keats's differing uses of this device in the three separate stanzas.
In the first stanza, Keats writes that autumn is a "close bosom-friend of the maturing sun." The Cambridge Dictionary defines bosom-friend as "a friend that you like a lot and have a very close relationship with." This means that such a friend can be of any gender. The activities that the sun and the autumn collaborate on involve the ripening of fruits, the filling of nutshells, and the growing of flowers for bees.
In the second stanza, Keats personifies the autumn as a laborer who gathers the bounty of the season by reaping, threshing, gleaning, and pressing apples to make cider.
The third stanza emphasizes the sounds of autumn, and so Keats presents the autumn as a sort of musician. The melodies that autumn offers include a choir of gnats, the bleating of lambs, the singing of crickets, and the whistling of the red-breast, which is a type of bird.
So, as you can see, autumn is indeed personified by Keats in this lovely poem. However, it is not necessarily presented as a woman throughout, but in different ways in each of the three stanzas.
https://dictionary.cambridge.org/dictionary/english/bosom-friend

https://www.bl.uk/works/to-autumn

https://www.poetryfoundation.org/poets/john-keats