Ideally, your bedside table should sit 5-10 cm lower than the top of your...

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

Ideally, your bedside table should sit 5-10 cm lower than the top of your mattress. This makes reaching for your glass of water or phone easy without straining your arm. In most UK bedrooms, this means aiming for a table height between 55-70 cm