said softly means you are speaking, but sweetly, and heartfelt. said quietly means it is less sweet, but still not loud or inaudible. whispered means you aren’t speaking at all, and it can have a negative or positive connotation, but more negative than softly. mumbled means it’s nearly inaudible, and has a more negative connotation.
try me, connotations are everything in writing; especially when conveying emotions.
I know adverbs are Controversial, but “said softly” means something different than “whispered” and this is the hill I will die on.