One of the pre-1900 texts is Geoffrey Chaucer’s The Merchant’s Prologue and Tale. Chaucer died in 1400 but his works were hugely influential during the 15th century, and some members of his family were closely involved in the Wars of the Roses. If you are studying Chaucer’s work, there is a helpful online dictionary of Middle English here.
You will find many parts of this website helpful in understanding the culture and context of the 15th century, for example: “Life in the 15th Century”
If you do not choose a medieval theme for your poetry you could do so for your non-examination assessment of a 2,500-3,000 word comparative essay.
The York Mystery Plays continue to be performed out of doors in the Medieval tradition.
You can listen to some of them here.
The Luminarium website has more detailed information about Medieval Mystery plays.