Posture for sleeping is important but can be difficult to change.
The ideal sleep posture is one in which all the normal spinal curves are maintained with minimum strain. The foetal position achieves this goal. The lumbar spine and pelvis should not twist too much and a pillow between the knees or thighs may be all that is required to avoid the common half tummy/half foetal sleep position.
When sleeping on your back, a pillow under the knees will keep the low back relaxed so that it does not overarch.
Sleeping is often a difficult adventure for individuals with neck pain. Finding just the right pillow can be a ‘nightmare’. The ideal pillow will cradle and support your neck without distorting its normal alignment. If your pillow is not supporting you properly, you might end up with recurrent “stiff necks”, headaches, or even referred pain to the shoulder, arm or hand. It is important to avoid using little or no pillow, which places the unsupported neck under strain all night long. It is equally unwise to use too many pillows or too firm a pillow, which pushes the neck up and stops the neck joints from moving properly whether you lie on your side or your back, your pillow must be soft enough to mould to your head and yet still fill in the space between your bed and your neck.
Remember, your head is bigger than your neck, so accommodating both without distorting your neck is the key. Sometimes an orthopedic pillow is helpful to fill this space. If you are a side sleeper and have broad shoulders, you will need a larger pillow than someone with narrower shoulders.
Finally, it is important to place your pillow between your neck and shoulder, not under your shoulder.