YES! MYRA THE MUSICAL!!!!!
For an intimate chamber musical how about the amazing book "Lying Awake" by Mark Salzman - it's about a cloistered nun who believes her intense migraines are visions from God and the choice she has to make to live with the pain or get surgery. It is an undiscovered gem.
Also, some of F. Scott Fitzgerald's short stories would be fantastic as musicals - "Diamond as Big as the Ritz", "Crazy Sunday"...
In the vein of "Myra Breckenridge" how about Djuna Barnes' "Nightwood".
Don't f*ck with me fellas. This ain't my first time at the rodeo.