I don't want to buy sanitary towels for people who menstruate either. I want to buy female products designed for women, because let's face it, if a towel was really designed to be genderless, it wouldn't fit properly.
There has to be better language - perhaps "women and trans men"? "People" doesn't give a gender identity to women or to trans men, so it doesn't really satisfy either. I understand completely that someone who no longer identifies as a female does not want to be referred to as a woman, but there has to be a better way of being inclusive.
Personally, I think we need a new multi-gendered word to describe women and trans men, exactly for situations like these. I don't think we have the right words yet, and that's what causes the anxiety rather than the actions.
I think if you still have a womb, you need to be able to refer to that biological fact somehow, so there's going to have to be an element of distress in getting that truth across. You might prefer to called a man than a trans man, but that doesn't explain why you menstruate; sometimes you are going to need to refer to yourself in a way that explains you have female parts.
Yeah, I still haven't got any further than "women and trans men." It seems the least upsetting to all parties based on the available words we have.