Aiming for a nightstand that sits 5 to 10 cm below your mattress-top is the...

https://amumreviews.co.uk/should-bedside-tables-be-higher-than-the-bed/

Aiming for a nightstand that sits 5 to 10 cm below your mattress-top is the golden rule for a comfortable reach. If your table is too high, you’ll constantly bump your elbows or hit your glass. If it’s too low, you’ll be straining to grab your phone