Said is a solid and useful dialogue tag. But here are also other examples you can use from time to time:
|“Don’t forget the keys, don’t forget the keys,” Dad murmured in his sleep.||Murmur||A low indistinct but often continuous sound, or a soft or gentle utterance.|
|“I bet he was murdered,” a spy whispered to his friend in the murmur of the hall.||Whisper||To speak softly with little or no vibration of the vocal cords especially to avoid being overheard.|
|“O-one moe,” the drunkard mumbled with his head on the bar.||Mumble||To utter words in a low confused indistinct manner.|
|“Put it down,” Mum lowered her voice.||Lower one’s voice||Keep one’s voice quiet but speaking clearly.|
|“Don’t let them see us, they’ll shoot,” the sentry muttered from the shadow.||Mutter||To utter sounds or words indistinctly or with a low voice and with the lips partly closed. Often to express anger or to complain.|
|“You need rest now,” she hummed.||Hum||Make a low and soft sound.|
See more vocabulary alternatives useful for writers! Poetic, amiable, angry, cute, and joyful said versions.