Loft means height. The right one depends on how you sleep, because the pillow is filling the gap between your head and the mattress - and that gap is a different size in every position.
- Side sleepers need the most height. The gap runs from your ear to the outside of your shoulder, which is the widest it ever gets. Too little and your head tips down towards the mattress.
- Back sleepers need the middle. Enough to support the curve of the neck, not so much that your chin is pushed towards your chest.
- Stomach sleepers need the least. Often almost none - the flatter the better, because your head is already turned sideways and any height adds twist.
The quickest check: lie down in your usual position and have someone look at you from the front. Your nose should line up with the centre of your chest and your chin should be neither tucked in nor tipped back. If your head is propped up or sagging down, the loft is wrong.
This one comes in 4 heights - 0.0, 1.0, 2.0, 3.0 - so there is a version of it for every position. BEDGEAR describe the range as four heights for stomach, back and side sleepers.