hi! i'm in year 13 doing combined english, geography and biology and i find that it's quite a good mix of subjects. apologies that i can't give any insight on psychology but...
following on from what s.m1 said, where do your strengths in exams lie? you might want to consider if you're strong with essay writing (english & geography) or if you're better suited to shorter but more in depth questions (e.g. biology). if neither is greatly weighted over the other, taking an essay subject like english alongside more science-y subjects can always be good as it breaks the examinations up - i like the fact that biology has more questions that are shorter and more application based whilst english are my long essay exams!
also consider what exam boards you're on for all the subjects and what texts you'll be studying for english. aqa biology has an essay on one of the papers which i did NOT want to do (i thankfully am on ocr), and my combined english course meant that all my texts were within time periods i was more comfortable with, rather than randomly being from the 1300s or something. if you have text preferences, do see what texts the place(s) you're looking at do as you will need to read them and know them and their context inside and out so you're gonna have to like them to some extent.
i would definitely recommend taking the epq alongside 3 other subjects too! i got an A in mine and found it very useful for hard skills - i would suggest doing it even more if you're looking to apply to uni!!
all in all, you wanna pick 3 subjects you know you can stick with for two years. you go into them in a lot more depth than at gcse and there is a lot more content for each course (especially biology), even though you're only doing three subjects. if you have any more questions, do feel free to ask. otherwise, best of luck choosing your subjects!!