To get your nightstand height just right, aim for the top of the surface to sit...

https://www.phone-bookmarks.win/for-the-best-reach-from-bed-aim-for-your-nightstand-to-sit-between-5-and-10-11

To get your nightstand height just right, aim for the top of the surface to sit roughly 5 to 10 cm below your mattress-top. This makes grabbing a glass of water or your phone feel effortless without having to overreach