Hi Lizzy,
I am originally from the States, but am living in the UK now. I am trying to get out of the 'office' grind. I am probably much older than you, but none the wiser when it comes to finding a career or self-business in the creative field.
You have the advertising industry experience, why don't you try working as a Sales Rep for a music manufacturer? I tell you this, only because I have a friend of mine who happened to fall into a Rep position with Fender Guitars. Some of the big guys at the top have seen how he works and the sort of person he is and are now grooming him to take over a high management position when the CEO or Executive VP retires.
Just wanted to suggest another avenue for you. Music promotions for a major record label or growing one might be another option to look at too.