This way, though, you can’t revert to colour later, so decide on your approach in advance.
If you usually shoot raw you’ll still get files with everything recorded by the sensor. Therefore, the image will be colour as normal once opened in your usual editing software, so you’ll need to do some work to render them mono. However, for mono shots straight out of camera, select JPEG image format and what you see previewed is what you get. This way, though, you can’t revert to colour later, so decide on your approach in advance.