I also don’t want my benefits to come at someone else’s cost, though.
Your guilt and concern about your own privilege are very male centred though, OP.
If female single sex spaces are turned to mixed sex, in theory to 'protect' the male people you feel are vulnerable, what happens to the female people who cannot use mixed sex spaces? I'm not just talking about the ones who will be very uncomfortable and unhappy - there's going to be millions of them, of all ages.
What about female people whose faith or culture means they cannot use any facility where male people are present?
What about female people with disabilities that mean they cannot reconcile the visual evidence and facts with a social lie they are expected to keep, or understand a massive, sudden change in social convention that may well be alarming for them? You'll find posters on MN with Autism who have mentioned how hard they find this, female people with dementia, Alzheimers, Tourettes, what about them if they can't use mixed sex facilities?
What about females who have experienced sexual assault and dv to the point they are unable to be in an enclosed space, never mind take their knickers off with a male in the room, regardless of cubicle doors in the way? What happens to them if they have not insufficient choice of toilets but no toilet provision at all, anywhere?
What about females like Tanni Grey, who has given evidence on this, or mothers with buggies, who cope in female loos by leaving doors open while they wee with a buggy in front of them, or catheterise themselves which cannot be done with the door fully closed through space issues? What about their privacy and dignity in a mixed sex provision?
Your guilt and concern not to have benefits over the male people you're concerned for is very kind of you - but there are female people who could desperately do with a little of that kindness or even to be considered as you give away their only possible access to a public loo.
We are going to have large groups of very vulnerable women, wholly excluded from any provision and the accompanying exclusion from society - with these women already being in hard to reach groups - to provide male people with more choice, safety and wellbeing.
Can you really not see the exceptional sexism in this that sees males as more important (and vanishes the impact on females) and leans on female guilt and negative socialisation that any male unhappy is their responsibility to fix?
There are many ways third spaces can be done, and improved on. Stripping females out of society isn't an acceptable solution.