Where have you been?! Should I start with my planned funeral soundtrack endless list?! Of course some are totally sad, others are of a raging sadness, others are bittersweet making you feel happy and sad at same time. Hope they work for you, they all work for me. Would also help if you said what did you find so far and if did or didn't work. You probably know all of the following, or dont know any, or hate all. I tried.
Within Temptation - Memories, Swan Song, Our Farewell, The Howling, Our Solemn Hour.
Evanescence - My Immortal, Is It Something Missing.
The Cranberries - No Need To Argue, Cordell, Electric Blue Eyes, Linger, In The Grave, Daffodil Lament, Ode to my family, Sorry Son, When You're Gone, Zombie.
Queen - Who wants to live forever, Show must go on.
Madonna - Mer Girl
Nightwish - Sleeping sun
Oasis - Wonderwall
John lenon - Imagine
Louis Armstrong - What a wonderfulo world.
And since you speak about piano, its not a voiced song, just melody, but this is one of my favourite instrumental sad songs: