Aim for your bedside table to sit 5 to 10 cm below the top of your mattress....

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

Aim for your bedside table to sit 5 to 10 cm below the top of your mattress. This setup makes it easy to reach your phone or water while lying down without straining your shoulder