Which specific area of
For most roles in psychology, you more or less have listed them. You could look into psychiatry, but that's more medicine than psychology.
The standard requirement to become a psychologist is to get a degree in psychology (either at bachelor's or master's) before doing a doctorate. I would ensure that the bachelor's/master's is BPS accredited, so you can manoeuvre into clinical psychology as well as psychology research. If the degree is not BPS accredited, your options are only limited to the academic.
See the following for finding BPS accredited degrees:
https://portal.bps.org.uk/Accredited-CoursesThe good news is that a good number of psychology related degrees out there are BPS accredited, but there would be a few that do crop up. In other words, I would always check the degree in the BPS search engine to double check.
The lowest entry requirement to getting into a BPS accredited degree is CCC at A Levels (I think) for a bachelor's, whereas it's a 2:2 (I think) if you're going for a master's. I am not sure why you think this is out of reach for you right now.
You would need at least a 2:1/Merit in your psychology degree in order to do the doctorate. If you fail this, then it's an even more of an uphill battle.
Competition for doctorates is stiff, so I would aim for a 1st class in a straight psychology degree where possible, along with quite a bit of relevant work experience in psychology and a GBC membership.