English literature, a modern language (perhaps French), History, and maybe Psychology would help, too.
I don't think Maths and the sciences are poor choices if you wish to study Law. Some even says that getting a great grade in Physics would act as a bonus as it proves your ability to reason and use your logic (not sure). Also, Maths and most of the sciences (Physics, Chemistry, Biology etc) are comparatively difficult A-levels (to most) and getting good grades in those subjects would perhaps increase your competiveness.
One solid advice: take solid A-levels.