I've just been asked this:
It’s me who am/is to decide.
It’s me who decide/decides.
Now, I believe the rule to be "a relative pronoun (here, 'who') must match its antecedent in number and person". So, using that rule, we'd get:
It’s me who am to decide. (I can live with this.)
It’s me who decide. (I'm struggling to live with this.)
This is not about whether the "me" should be "I". That's a different point.
I'd love some support for these answers or an explanation of why they're wrong.