Maybe sociology as it goes the best with psychology. I also want to do psychology at uni and am going to take biology, chemistry and psychology. Maths as a pure a level isn't for me haha. Most Unis require at least one science so maybe do biology. However, some universities accept psychology as a science but if you don't have bio,Chem or physics then you will limit your university choices. I recommend researching different unis you are interested in and look at there psychology requirements as it really does vary. Based off of that and what you are interested in, you can decide your final subject x hope this helps x if you decide you won't take a science then I strongly recommend sociology to go with your other options