I know I sound like an idiot who has no idea what to do with her life but I think I'm finally getting somewhere in terms of planning my future, so please help- any advice would be greatly appreciated!
PPE does sound like it'd be a good fit for you, provided you're interested in Economics too.
If not, I do know of a few joint hons Politics and Sociology courses- Bristol, Warwick and Newcastle do them. Politics and Philosophy/ Psych and Philosophy are also combinations I've seen around. My friend currently does Politics at the University of Essex, apparently the department there is fantastic, so you might want to look on their website. Good luck!
With all these, check carefully that the particular combinations in which you are interested can be studied together. If you take Psychology, you also might want to check whether the degree is BPS accredited.