I can't find where I read it - I think the problem would be there has probably been very little if any study done into the effects of the combined pills on lactation at 2 years post-partum. Most of the research is done in the 0-6 month bracket - which it makes it very difficult to make a decision.

I think if I was you and Yasmin will benefit you from the PCOS perspective - I would take a what will be will be approach and take it - and accept that there is a possibility it will end your BF relationship, but is also possible that it won't. (given the age of your DD - if she was younger than 18 months then depending on the problems PCOS is causing I might well wait till later before starting combined)