Have you had any expert hands on /manual therapy for the tight /spasmed muscles?
I had thumb wasting for a short time, but after we got my muscles spasms relaxed in my neck, that went away..

I had severe spasms in my neck muscles and it pulled my top rib up and they got stuck, multiple PTs nor a very good DC didn't notice that, until I sought out another assessment by a PT instructor , he tried a top rib mobilisation to drop them.
They dropped 1/2 " and so much pain & other arm use limitations just went away.. I drove the 45 mins home without have to switch hands on the steering wheel.

I also had a lot of trigger points but could get most of them using a tennis ball against the wall or down on the floor. You tube shows many ways to do that..
A muscle can not be fully released if it has trigger points ..
(see all our sticky threads above the TOS main page for lots of info)

Some at home things to try-
https://www.neurotalk.org/members/100-albums422.html
Yoga corpse pose

Sharon Butler's RSI website has some gentle stretches & breathing suggestions..

Some supplements I found helpful- MSM , Grape seed extract

Pilates might be too intense (long muscle hold postures?) unless the instructor has a knowledge of rehab & injuries/pain reduction..

I'd suggest finding some very good PTs or DCs and try a few to compare , focus now should be pain & symptom reduction, before any strengthening ..

Did you have MRI of the neck area to rule out bone anomalies or other c spine issues?