Thank you! If you can’t find it, that’s alright.
I’ve sent out feelers among my medieval history friends for a good link. I have the lengthy prayer in my possession (medieval Catholics loved long prayers and Masses!) but here is a touching section of it written by his personal confessor, John Roby, who I believe died at Bosworth as well. The prayer was NOT written at Bosworth or for Bosworth (although undoubtedly prayed by the King at that time) but when the King had lost his wife and child within a very short interval. It is very good for suffering souls:
“Lord Jesus Christ, deign to free my, your servant King Richard, from every tribulation, sorrow and trouble in which I am placed - hear me, in the name of all your goodness, for which I give thanks, and for all the gifts granted to me, because you made me from nothing and redeemed me out of your bounteous love and pity from eternal damnation to promising eternal life.”
It is written in English (the language he preferred) although he spoke and wrote Latin. Portions of the prayer are typical medieval “boilerplate” but this is the most famous sequence of it.
I hope to get the entire thing to you. From an historical viewpoint, it is quite interesting.