This is only specific to the Yuan Dynasty Mongols, but I don't think the Ming-era official history of the Yuan Dynasty, the Yuanshi, has ever been translated into English. This is the basic starting point for any information on the Mongols in China: the way they ran the country, their military, their customs, and so forth. It has source material needed if you want to know what the Mongols did in China.

The Yuanshi (History of the Yuan dynasty) and the Jinshi (History of the Jin dynasty) are history texts officially compiled by state historians from primary sources. The Yuanshi covers the Mongols during the Yuan dynasty, while the Jinshi discusses the rise of the Mongols and their defeat of the Jin (it also covers the entire history of the Jurchen Jin dynasty). Neither texts have been translated into English, nor have sinologists translated the primary sources that were used to compile the texts.

It's a shame that so few of the primary sources have been translated. The Secret History of the Mongols is essentially imperial hagiography and a folkloric account of Mongol history. Primary sources written by Jurchen officials sheds light on the less glamorous aspects of Mongol history. For example, prior to the conquests, the Mongol tribes were Jurchen vassals, an inconvenient fact that is rarely mentioned in sources sanctioned by the Mongol government.