For the most practical setup, aim for your bedside table to sit 5 to 10 cm...

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

For the most practical setup, aim for your bedside table to sit 5 to 10 cm below the top of your mattress. This makes grabbing a glass of water or your phone effortless while lying in bed