Hello! In the exact same position as you! I do psychology, politics and law at A level, and I am also torn between psychology and law at uni.
It might be a good idea to look at what you want to get out of each degree, ie, what do you want to do post-graduation? You could look at career prospects for each degree and see what appeals to you, you could also look at the modules you would be studying for each degree and which appeal to you more.
You could also draw up a pros and cons table for both degrees. Either way, if you took psychology, you could always do a GDL afterwards. Or if you did law, i believe there is also a psychology conversion course. Of course it would mean an extra year of study though.
Hopefully this helps?
(In terms of work experience, look at volunteering with the NSPCC, or the Samaritans)