My biological sex is female. I don't think 'woman' is as simple as biological sex, that is where we differ obviously.
I think the definition of 'woman' is currently in flux, that is why we are all having such fierce debates about it. This is a normal part of the norm life cycle -- the contestation over how to define social norms. At some point a consensus will re-establish itself.
I suppose for me a working definition would be anyone who lives their life as an adult human female, whether they were born as such or not. Yes, there is a certain fluidity to the definition but I think that's okay, this is normal for most aspects of identity.
I mean, can you define British? Who is a British person? What if they are born abroad to British parents, can they still be British? What if they come to Britain in their 30s and live here for years, can they become truly British? Interestingly, on that last question, some British people would say yes and some would say no.
And yet, despite this apparent muddiness, there is not really a problem in understanding what we mean when we say things like, we want to improve the lives of British people, or we want to help British children get a better education. We don't all stop and say hang on, how are you defining British? We focus on the main issue.
I think that's really what feminists like me want. We just want to get on with things. There is not much confusion, in real life, about what a woman is or what we mean when we talk about women's rights. Trans women are a tiny minority of women in the UK. Yes, there are important issues around inclusion, but these are not insurmountable.