I saw a physical therapist specialty was breast cancer surgery patients, prior to my surgery. She took range of motion measurements etc. I did that so she had a baseline of where I should possibly get back to. 4 weeks post surgery I started PT with her. It made a world of difference for me. Just a thought. I used everyday tasks to raise my arm for stretching i.e. using my arm to reach coffee cup on second shelf, wiping down shower, I used that arm and took note of how high I could reach each day, as the steam allowed me to see measurement. I had right side mastectomy and am right handed, so the thought process wasn’t too hard, but had to be careful not to overdo. It is easy for us humans to compensate, if we think pain might be involved. Blessings for your upcoming surgery.