I think that you've already started math -- by playing games, cooking, finding patterns, etc!
We use Singapore also.
It really stresses understanding how numbers work rather just computing and memorizing. When my older DD was 5, she did Early Bird 2 and really enjoyed it. Early Bird 2 is a lot more fun that Primary 1, and it only costs $15, so I would let your child start there even if it is very easy and only takes a couple of month to...