John Keats - Poetry Foundation
https://www.poetryfoundation.org/poets/john-keats
The Poetry Foundation page for John Keats, which includes further biographical information and links to poems and essays.
Chapman's Homer - The Illiad and The Odyssey
https://archive.org/details/iliadandodyssey00homegoog
A digitized edition of Chapman's Homer.
On First Looking Into Chapman's Homer - English History
https://englishhistory.net/keats/poetry/on-first-looking-into-chapmans/
An article that describes in detail the sonnet's back story, and includes an image of Keats' original manuscript.
Letters of John Keats to His Family and Friends - Project Gutenberg
http://www.gutenberg.org/files/35698/35698-h/35698-h.htm
Keat's letters to his family and friends, fully available at Project Gutenberg.
A Possible Keats
https://www.nybooks.com/daily/2017/07/24/a-possible-keats/
A short story that takes Keats' life as its inspiration.