I post this in case it is of any benefit to others. Not to patronize anyone.

1. My dx is bilateral TOS. My pain is on my left. My right though is worse structurally than my left.
2. Pec Minor syndrome.
3. I do not have a cervical rib.
4. Rounded shoulders because of tight pec minor and weak Rhomboids and Mid-Traps. (typical of those with rounded shoulders)
5. Slight scapula winging.
6. Lieing on foam roller lengthwise under spine...allow shoulders to drape back...add weight if not uncomfortable. Head on one end of roller, butt on other end. Suck in gut. Legs bent.
7. Chest opener exercises. Ask a Yoga instructor what these might be.
8. Practice RETRACTION of the shoulders (pinch blades back). Watch any movement or household stuff that requires PROTRACTION of the shoulders (concave chest...accentuating rounded forward of shoulders). Try to minimize the latter. Actually try to AVOID the latter.
9. When picking up stuff on the floor (requiring you to bend forward) WATCH where your shoulders go...probably they automatically roll forward....DON'T let them. Start with shoulders down and back and try to maintain that posture as you bend forward.
10. Carrying heavy or even moderate weight objects in front. Tension will be on one bicep tendon and pec minor..this will PULL down/forward on CORACOID PROCESS (CP) which is part(front) of scapula...the Brachial Plexus set of nerves which is compressed in TOS passes right under this CP. Thus any rolling forward of the Shoulders will cause compression and flare ups.
11. Foam pillow lengthwise against spine for sitting. Especially useful in cars with "bucket type seats" where shoulders are pushed forward. Use the pillow and try to watch the posture during driving.
12. Head position. It should be in line with spine...NOT forward with chin sticking way out in front. Cervical portion of spine should be straight up and down...chin level or slightly down, chest lifted up, shoulders down and back. Yes, belly breathe but by lifting the chest and retracting the shoulders you are CREATING MORE SPACE for the BP to pass under the CP. More space, less compression.
13. My mantra: Shoulders down and back, retracted, blades pinched...neck not out front....ever.

Hope the above helps.

14. P.s. Another tape trick. Get a friend to tape your blades ...one piece of tape horizontal from one blade to the other about middle scapula or lower level...start with your blades retracted slightly (good posture)..then apply tape. There should be some tension on the tape such that if you relax too much you will feel more tension in the tape to remind you that you protracted the shoulders rather than retracted them.