As for how to use a pillow the goal is simple. Have it positioned so as to comfortably support the body as close to neutral as possible.
For back sleeping the pillow is moulded to make a divot in the middle. This creates a glove around which the head rests. The neck should have it’s natural curve supported which is tailored to the individual. For some this might be very little plumping of the pillow under the neck while for others significantly more.
The depth of the divot also needs to be tailored to one’s adopted posture. If posture is good the head should rest comfortably on the mattress. This would leave no loft directly under the head just the thickness of the sheets encasing the pillow. If there is forward head carriage which is more common than not then a certain amount of thickness under the head is needed. For some people with arthritis or habituated poor posture this could be 10 cm or more.
For side sleeping the pillow needs to be plumped up so the neck and head are parallel with the mattress. This depends on how broad the shoulders are and the softness of the mattress.
Shaping the pillow to best support the neck may sound complicated especially if time is shared between back and side sleeping. It’s not. Once the basics mentioned above are understood shaping it is a simple and quick process. Mould the pillow as for back sleeping and the loft created on the sides looks after the needed support for side sleeping.
Typically, a little time in needed tweaking the pillow to achieve the ideal postural support. The depth of the divot and where the divot rests within the pillow are important here. The depth of loft on the sides and the portion of the pillow under the nape of the neck may also need to be finely tuned.
A good idea is to lie down to trial the pillow. Include rolling from back to side in both directions. This will help to ensure your posture is comfortably supported in both side and back sleeping.
A final point to ponder when deciding on a pillow, or mattress for that matter, is off gassing. There are lots of health risks that are not well understood. Off gassing from foam is one of them. For this reason, I lean towards to caution. One more strength for the wool pillow.
And on that note I wish you all a good sleep.