Congratulations on your weight loss! You might like to try some port de bras movements from ballet.
Here is a nice tutorial that explains the movement and also gives hints on how to hold the shoulders, elbows and hands. This type of movement can really help the arms and shoulders. You will feel it in the back as well, when done correctly.
https://youtu.be/2m7mYKRCxvo
If you don't want to click on an unknown link you can search for the video in YouTube by putting in Ellen Davis ballet, or Teaching Classical Movement with Ellen Davis. That should pull it up. I'm not affiliated with Ms. Davis, but used to be a dancer years ago and ballet creates lovely arms.