hey! my sister is currently doing psychology at uni and has told me that if she wants to be employed with it she'll need at least a master's. If you think getting a BA and then a master's is something you'd enjoy then go for psychology! but if not maybe look at other career avenues?
In terms of "can I do something unrelated to my access for degree", my understanding is that it kind of depends. I did an access for art and am doing on to do art at uni and my understanding is that if a course asks for say x amount of ucas points but no specific subjects then you're good to apply and do it if you meet the ucas point threshold (but bear in mind you'll need to explain why you want to do something different to the thing you did your access in, probably in your personal statement) but some specific degrees, usually technical/stem ones and very competitive ones, want you do have done specific subjects at either access or a-level. so it kinda depends!