Hi trix,
as much as possible try to keeep some amount of movement - keeping arms curled in is not to good for circulation or maintaining muscle as you mentioned.

slow and gentle movements to keep your range of motion as best you can.

Have you tried the laying on the floor thing?
I'll repost it here-

For passive gentle stretching - try
Laying on a rolled up towel or foam cylinder {approx 6"x30"}
or flat on floor if that is more tolerable for you
let gravity drop shoulders and open chest
{pectoral muscles } and use diaphramatic breathing to relax and release into the stretch

lay the length of the spine on the cylinder /or floor with a small pillow for head & neck if needed {pillow was recomemended for me because of the c-spine issues}

just relax and let shoulders drop and chest and armpits will release and stretch - place arms at a comfortable position 15-20 minutes as often as you can.

If you have mild low back troubles put a pillow under knees or raise them.
If you have any spine problems check with doctor before doing this.

I need to go do this myself - haven't been able to since we had everything crammed into living room while redoing kitchen.