Cacao beans were the main, everyday currency. As a guide to their value, there’s a surviving list of market prices from 1545 (a generation after the Spanish arrive) amongst which are: a rabbit cost 100 beans, an avocado 3, a large tomato 1 and you could get 5 green chiles for one bean. There was even a tradition of counterfeiting beans.
Cotton cloaks (quachtli) were effectively a larger unit of currency, with particular sizes being assigned particular values - for example, a cloak of one size might be worth 100 cacao beans. One estimate is that a commoner in Tenochtitlan could survive on 20 quachtli a year.
As for gold coins, these would certainly have been within their metalworking capabilities - many of the few surviving gold pieces are exquisite - but it’s just never something they did. More generally, gold items were common alongside other luxury goods in the system of tribute that was a major feature of their society.
There’s a good discussion of the Aztec economy in chapter 5 of The Aztecs (Blackwell, 1996, 2003) by Michael E. Smith.