The focus should be on preventing people from ending up in those prisons in the first place, by creating a more equitable society. Then, when fewer people are going to prison, it's easier to make sure they're humane.
Completely agree that we need to spend more resource on prevention. I see decent prisons as part of prevention too (the greatest cost of offending is reoffending, about 80%). But yes, stopping people ending in prison in the first place is essential.
‘having better prisons can be an indication of a better society’
I don’t think I quite said that. Dangerous prisons contribute to a dangerous society, but there are many other contributory factors.
but I think that the way a society treats its women, children, and disabled is far more indicative of whether it's civilised than how it treats its (mostly) male criminals.
I don’t really understand this. It’s far easier for society to treat the vulnerable well (someone has already said). But also you haven’t listed men at all, so in your view society should treat women and children and disabled people well, but able bodied men, who cares? I fail to see how that would lead to a healthy society without male violence.