For the most comfortable feel, aim for your nightstand to sit between 5 and 10...

https://sticky-wiki.win/index.php/How_Far_Should_the_Nightstand_Be_from_the_Bed_Edge%3F_The_Expert_Guide_to_Bedside_Ergonomics

For the most comfortable feel, aim for your nightstand to sit between 5 and 10 centimetres below the top of your mattress. Most standard bedside tables in the UK range from 55 to 70 centimetres tall