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 glass of water or phone without straining your arm. Most UK beds look best with tables between 55 and 70 cm high