I would suggest looking into ultrasound guided botox injections of the pec minors, anterior scalenes and middle scalenes.

It sounds like your scalenes and pec minors are tight (this will also make the traps tight, but the botox injections in the other muscles will loosen up the traps, not sure why, it just does).

In the meantime, try using a heating pad and a soft cervical collar together. Put the heating pad or even pads on the front and/or sides of the neck and strapping it on with a cervical collar. Most cervical collars are 3" but I found a 4" one that stretches the neck even more. I used to do this along with taking my muscle relaxants at night pre-surgery and it helped more than using the heating pad anywhere else or the cervical collar alone.

In order to keep the shoulders back, do "pushups" against the wall to strengthen the rhomboids.

Also rubbing oils into the neck and stretching it side to side helps - I recently tried mustard oil.