When you find a shirt that fits exactly the way you like, you want to have a bunch of them. Mira from Sewing The Littleheart Collection made a shirt for her mother based on a shirt with a perfect fit for her. It’s fitted through the shoulders and bust, but flares out to a drapey hem. She shares the pattern (size large - XL) and tutorial for making it. If you need a different size, you could draft your own using a t-shirt that fits as a sizing guide and her pattern as a shaping guide. Get the pattern and tutorial.
[photo from Sewing The Littleheart Collection]