Hi happy2023,
I'm a physical therapist and I wanted to give you my thoughts on this because I work a lot with people who have compression fractures and osteoporosis, I also know about the vest because I have bronchiectasis too! If you don't have much pain, they often allow it to heal on it's own and a brace is not aways recommended because it can cause muscles to weaken. When you're able to return to using the vest, I would recommend doing it in a standing position if you can because in sitting the spine is flexed and this adds compression to the vertebrae. Ask your PT will teach you about positions to avoid, especially avoid forward bending. Hope you feel better soon, take care!