One of my Patchwork class ladies is semi crippled with a Arthritic back and hips so I made her a oblong cushion, out of flannel bits n pieces and added a big pocket, then popped in a Orthopedic Ice bag, a bag of frozen peas will do the same, and placed it behind her when sitting on an upright chair. After 20 - 30 mins I replaced it with a warm Lavender scented wheat bag, the relief she got was immense, I think she loves me now ;)
For shoulder tension try putting a cold pack on first, for just 20 minutes or so and then use your warm wheat bag, you will really get a whole lot of benefit, don't ask me how I know,
Signed a Cuff Tendinitis sufferer :(