PillowTies recently sent me an interesting piece of travel gear to try which I never thought could have existed. If you are a traveler like me who uses a pillow to sleep on long distance flights but does not like the dangling pillow then this is the exact gear you are looking for. It holds the pillow vertically forcing all the neck movement to be in the horizontal plane. So, one can comfortably sleep straight or sideways while still ensuring that the neck remains in a good shape. In fact, even when I am not sleeping and just playing with my phone or watching videos, I have enjoyed its support in keeping my neck straight. It is relatively sleek and hence would easily fit in your travel jacket or backpack pockets. I, first, thought that this might not work on all different seat configurations but I have tried it over many domestic airlines in the US and it has always worked.
Note: The initial installation does take some time to get used to, therefore, initially, I would recommend using a PillowTie only for long flights (4+ hours).