Maybe you're used to sleeping on a thin pillow filled with duck feathers. But just because you're used to it doesn't mean you're sleeping in the correct position. One of the main factors influencing your sleep is your pillow. When you decide to buy cushions online, remember the tips above: The correct sleeping position is the one in which the spine is completely straight, therefore you should choose according to your sleep position so that the spine remains straight when lying on the bed.