I feel like it's pretty weird that our characters just go from stone tools to ancient/magic tools with almost nothing in-between.
That's why I'm presenting the idea of ores and such.
They'd be found mostly underground (duh) but it'd be also possible to gather them from the ocean as an underwater junk.
Then there'd also be a smelter or oven or smth like that you'd use to melt these ores into bars. And boom now you have metal tools.
Adding metal would also allow for some new structures like… barrels or… buckets… maybe a new cooking thingy