You will need BONING. Historic corsets used whale bone to stiffen corsets. Modern corset makers use steel. You can get steel bones either as flat steel and spiral steel - do research, as different types of corset and different corset makers have their own preferences. Plastic bones are also a cheaper option.
You can find a good guide to other tools at [Foundations Revealed](https://foundationsrevealed.com/).
Sample supplies list:
* About 0.5 meter of core fabric ([see Fabric options](/docs/patterns/cathrin/fabric))
* About 0.5 meter of outer fabric ([see Fabric options](/docs/patterns/cathrin/fabric))