For the best balance of comfort and style, your nightstand should sit level...

https://www.coast-bookmarks.win/the-golden-rule-for-bedside-tables-is-comfort-aim-for-your-table-to-sit-about

For the best balance of comfort and style, your nightstand should sit level with your mattress top or just 5 to 10 cm below it. Most standard UK beds work perfectly with tables between 55 and 70 cm high