For the most comfortable reach, aim for your bedside table to sit level with...

https://mega-wiki.win/index.php/The_Perfect_Bedside_Table_Height_for_Back_Sleepers:_A_Practical_Guide

For the most comfortable reach, aim for your bedside table to sit level with your mattress top or just 5 to 10 cm below it. Most UK beds work best with a table height between 55 and 70 cm