I sing and play harp. It takes a while to get the hand of it…you really have to have the chords in your fingers and have the song in your “body” :). Sounds a little hoke-y, but works. I usually sing sitting down, but have done some gigs with a harpsicle standing up.
I am primarily a harpist, not a singer. I have studied North Indian classical singing instead of Western and they sing sitting down. Maybe that method would help?
all the best in noise,