By all means boycott stores and certain producers if it makes you feel better.....and you don't fee unnecessarily deprived as a result; but I'm not sure you are really doing anything much more than cutting your own nose off, in this instance. This is not to minimise the issue - but to take a more strategic view of it.
Not buying a washing machine, for example, from John Lewis because they sometimes permit male bodied people into the women's changing rooms doesn't follow logically...... certainly is not consistent with being prepared to vote for parties that have supported/do support Gender Self ID ( & they all do) simply because you like some of their other policies......It is at the level of policy, at a national level, that has the greatest impact on behaviour further down 'the food chain'.
I'll continue to shop at John Lewis - because I like it, and do most of my household ( & clothes) shopping there; although I've already brought up the issue of changing rooms with them ( hence I know they've already been doing this for many years) and will continue to do so.
Gender Self ID is the biggest issue, at present - along with what is being taught and encouraged in schools. Self ID will increase the numbers of men who legitimately feel they can access women's spaces - and who have the full legal backing to do so.
In this case I think the war will have to be won from 'the top down', not by thinking that individual organisations, especially national chains and corporations, will go against the flow and general consensus of 'best practice'. Because I don't think they will.
In the meantime, maybe, like in my local branch of john Lewis - they will make some attempt at separation between cubicles and areas so as to be as discreet as possible and not upset their female customers.