One unique first-hand source on the Mongols can be seen in The Story of the Mongols: Whom We Call the Tartars by Friar Giovanni Carpini. (translated by Erik Hildinger) The cover with a picture of a Mongol soldier is itself worth the price of the book ! - https://www.amazon.com/Story-Mongols-Whom-Call-Tartars/dp/08...

Overview of the work on wikipedia - https://en.wikipedia.org/wiki/Ystoria_Mongalorum

You will love this book: The Story of the Mongols Whom We Call the Tartars by Friar Giovanni Carpini.

The cover itself is worth the price of the book - https://www.amazon.com/Story-Mongols-Whom-Call-Tartars/dp/08...