Brit looking for a visa to move to Mexico (Mexico City)

Hi there guys,
I just wanted some advice on what are my best options for moving to Mexico city.
I am from the UK and currently live in Madrid, Spain. I am looking to move to Mexico city to be with my girlfriend (she is Mexican).
I guess I am looking at getting the Work permit visa but also wanted to know the case with people entering on just a visitors permit and then gaining employment therefore starting the process to change their status (although I realise this has changed since Protected content

Thanks for reading and I hope you can help.