A Gambeson (spelling varies as this word predates the OED) is the second to third layer of clothing worn under armor, the first layer may or may not be "small clothes" or underwear, the second layer may or may not be other clothing such as trous or trousers and a tunic or shirt.
Step 1: The History
The Gambisons primary purpose is to provide padding from impact , and secondary is as a insulating cooling layer.
Historically in Europe it would have been made from wool or if your were fabulously wealthy linen, cotton or even silk. This may apply in Asia, I do not know.
Many argue that the lozenge or diamond pattern quilting is not historically accurate, but I'm not so sure, I've seen a chess piece from the Isle of Lewis that clearly depict a diamond pattern and the pieces carved there demonstrate a high degree of accuracy. Additionally the Bayeux Tapestry show something that may be diamond pattern, the diamond pattern is logical since it holds the batting in place very well.
Regardless of historical influence, diamond pattern sewn padded material is readily available at most fabric stores and is acceptable to average observer as not dispelling the illusion of authenticity.
If you must be historically accurate this is not the project for you, I have no primary evidence but would be happy to hear from someone who does.