In the UK, it does not generally work in terms of you finding an advisor to help you. You need to competitively apply for a post, or apply self-funded explaining what you're proposing and why.
I have to confess if I get an email along the lines of 'can you help me' from a prospective PhD, I'll provide a bit of loose guidance then cut communication as otherwise (from experience) it becomes an unpaid mentoring role - which, rarely, is ok if the applicant has dramatically clear potential, but not something you could reasonably have time for from everyone that asks.
The fact you seem to want to do a PhD but not know what in is a bit of a warning sign to potential supervisors. You need to cultivate your interests and be coming in with 'I'm extremely interested in x... and have been reading a lot of y, and z'. An experienced supervisor will know it will be your passion for the subject that will get you through the late nights, and if you don't come across as knowing specifically what you're passionate about and just want the paperwork, you will be on the back foot from the start.
I think nobody can tell you what you're interested in, or passionate about. But that's really the essential first step to a successful PhD.