YESSS!! I looked in the cupboard randomly and found a slow cooker.
I'm so going to make this soap.
This is also good in that I can probably make my soap in the garden now, which means less arguments (last time, something fell out the cupboard and smashed in my lye mixture, which splashed all over the varnished worktop and the aluminium surface of the microwave. Not good.)
I'll let people know how it goes. Thank you everyone for the help!