Sorry for the delay in reply!
I am using 115200 as my baud rate, as recommended by the guide I am following.
In GRBL Control this lets me connect and change values:
And in the Arduino serial monitor, it connects and displays the firmware I am using:
Though I can't run any commands... (Probably because I am using non-standard firmware at the moment?)
So I believe the baud rate is set correctly.
What should I look at next?