To be honest , law is very universal in that any a levels will help with law. so don’t worry if you about finding the perfect a level course to go with law ! However from what I heard, sociology a level has a lot of law related content e.g crime and deviance. It is also a essay based subject so will help you prepare writing more longer essays.
However, business is also a great option especially if you want to go into commercial law.
I currently do psychology a level and there are aspects which do help for example we learn about eye witness testimony and the inaccuracies of it.