Why get a pillow in your size?
We don't all wear the same size shoes because we are different sizes
So why should we sleep on the same size pillow?
You can find your shoe, dress, shirt, trouser and even bra size by getting measured
You can now get measured for your ideal pillow size too
You don't buy shoes in the right size because you have foot problem
You buy shoes in your size so that you are comfortable and so will avoid getting foot problems
Buy the right size pillow for the same reasons. Not necessarily because you have a problem but simply so that you are more comfortable and can avoid problems brought on by poor posture and by poor sleep.
The best pillow is the one that is right height and will keep you better aligned. You will not toss and turn in bed as much because you will be more comfortable. You will spend longer in the deep restorative part of the sleep cycle and so will wake up better rested and feeling more refreshed.