I read a lot of history books, but I don't recommend going directly to the history of the Yuan Dynasty and the history of Feini Zhi's world conquerors. These books are very old, and there are some fallacies in some places. I recommend some books to you:
1. Biography of Genghis Khan, Zhu, People's Publishing House
2. Mongol Empire, Zhu, People's Publishing House
3. The Biography of Kublai Khan, Li Zhian, People's Publishing House
4. The secret history of Mongolia sells very well, but it is very expensive, like more than 60 yuan. It was written by an unknown author during the Khan period in Wokuotai, and it is the basic data for studying yuan dynasty history.
Also, I want to talk about the works about Mongolian history written by foreigners. I have read Genghis Khan and Grassland Empire by Jules Grosset, and I feel obviously inferior to Zhu's book, and the translation is very poor. I suggest not reading them.