Step 1, go talk to your math professors. I'm sure they will be happy to write you letters, probably excited that you're interested in pursuing grad school.
Find one teacher that you liked, that you felt you learned a lot from and stop by his office. Explain your situation and ask his advice. My feeling is you should maybe get all of the recommendations from math professors, but 2 math/1 philosophy may work. I'm sure your current boss would write you a very nice recommendation, but imagine it from the school's standpoint: why is this person able to judge whether the applicant has the ability to make it for a Master's/PhD? Being a professor, having a PhD yourself, being at a school with reputation, having research.. those things carry quite a bit of weight.
It's not too late to build personal relationships.