Perhaps this might help:
When the subject is emphasised, who (referring to a person) is possible instead of that; e.g., It was my mother who threw...
When the emphasised subject is a pronoun, there is a choice between subject forms I, me, etc) and object-forms (me, him, etc); e.g., It was I who ... It was me that ...
Object forms are more common in informal English.
- For Teachers