I don't think choosing further maths A level is a good idea unless you got a top grade in GCSE. If you want to work in accountancy, it would make sense to take applied or decision mathematics. That said, when I was doing work experience at an accounting firm, I didn't see any maths being used that was beyond what a GCSE student with a pass could do. You should talk to your careers adviser about the accounting course to see if it suits you. If you think you'll enjoy it, and it's possibly something you want to do in the future, then go for it.