Hi!

If you are opting BA Maths then the best subjects to have with it are:

1. Maths, Economics and Applied Statistics. These three subjects open many career options in field of arts plus mathematics.
2. Maths, Economics and Computer Application. It is a great combination as despite of being Bachelor's in Arts it would help in getting into technical and IT sector.
3. Maths, Economic and psychology. You can have a career in science as a clinical psychologist and psychology is a great subject.

These subjects make best combination for BA Maths but they might get a little hectic. However i believe this will suit you perfect as you have interest in Maths. I hope you find this helpful.