If dd is 17 months she is only likely to want a bit each day, and be weaning soonish, so it shouldn't matter to much (though if you want to carry on, thats great). I haven't done this myself, I had a Mirena fitted, which suits me very well indeed (I have a history of depression) which is fine with breastfeeding.
Hi. I had an appointment with a GP that specialises in contraception to ask the same question. DS is 14months. She said that supply should cope with a low estrogen pill like Mercilon or Femodette and tbh if it goes I wouldn't be devastated. However she said that there had been very little research on the effects of estrogen, albeit in very small doses, on the developing brain of a baby. She said any risk would be small but, all considered, she thought that my reasons for going on the combined pill probably didn't justify the small risks. So I've decided not to for now although I would really like to!
If you are looking to ttc in the next year perhaps the better thing to do might be to come off the pill altogether so you get your natural cycle back and use condoms in the meantime? A bit of a pain in the arse but if it's only for a few months it might be less of a pain than starting on a new pill and then coming off it again.