I think one of the best (and very current) articles about how to break into QF (for any kind of background) is:
"On becoming a Quant" by Mark Joshi
For your special background in mathematics see this excerpt from section 9:
The main challenge for a pure mathematician is to be able to get one’s
hands dirty and learning to be more focussed on getting numeric
results than on fancy theories. The main way to do this is to
implement pricing models for practice. If this doesn’t appeal you
aren’t suited to being a quant. There are quite a few ex-pure
mathematicians working in the city so it can certainly be done but
there is some prejudice in favour of applied maths and physics people.
Generally, people tend to hire people who are like them so if you can
find anyone with a similar background working in the city, apply to
them.
I sometimes get asked by people whether they should do a pure maths
PhD or a financial maths one. If you are absolutely sure you want to do
derivatives pricing then you should do it in financial maths. (Yes, I
am taking PhD students but have no capacity at the moment.) If you
aren’t sure then don’t. A good compromise is to do stochastic
calculus, this is a hard area which will give plenty of intellectual
stimulation and leave you very well placed for working in derivatives
if you ever want to make the switch.