May have been mentioned elsewhere, but surely making the men's amenities mixed sex, whilst keeping the women's single sex would be the most inclusive?
More TMs pass than TWs, so they could use the mixed sex without worry. All those women who "don't mind sharing toilets/changing rooms" could use the mixed sex area, so that they can ensure that TWs will feel validated when they use it too. This would then leave the single sex women's, providing a safe haven for any female that needs it, be it for religious or any other reason.
As an added bonus EI, Pip Bunce and any other gender fluid types, would be able to use the mixed facility regardless of their gender "mode". They could even flip genders mid-wee, and would be safe in the knowledge that it wouldn't cause discomfort to anyone else.
Might even help keep the queues down in the women's too, win/win n all that.