Please define what good money means? Office jobs make pretty 'good money' if you ask me, such as if you worked for one of the big 4 accounting firms etc. First year out is like 60k or so I hear. Otherwise, seeing as how you seem to like maths, engineering or actuarial studies may be the degree for you. I believe materials/chemical engineers make quite a bit. Actuaries too, but the maths is most likely (I'm pretty sure but I shall save myself in case I'm wrong) NOT the maths you know and love right now. So you may need to research that a bit more.
To become any of these:
- office job: requires usually a decent resume and preferably a bachelor in something that is mildly related--majoring in accounting and finance is probably preferable in a bachelor of commerce
- actuary: I believe there are both undergrad and post grad courses in this. For example, in melbourne the desired pathway is probably the bachelor of commerce, majoring in actuarial studies.
- engineer: bachelor of engineering or master of engineering.