Sorry if I’m being stupid, but I was wondering if there’s a way to organize your inventory more quickly than one item at a time. I can’t find the option to/page if there is.

From the menubar at the top,

Commerce > Your Shops > Shop Name (qs)

...click on the link after the shop name and it'll send you to the Quick Stock page. Hope that helps. :)

Ohh, it's located in the shop?! I was looking everywhere but... That completely answered my question, thank you.