I need some sort of work experience or extra-curricular activities that revolve around psychology to be able to apply for a good university (as an undergraduate)...
You don't need to have work experience related around psychology to apply for undergrad. The more important thing would be to do extra reading connected to psychology outside of what you cover in your A Levels
I always think that it's quite impressive on a personal statement when people link volunteering they've done (i.e. at a mental health charity) with some further reading (i.e. made you want to read more about aging and the brain or dementia).