For the most comfortable setup, aim for your bedside table to sit roughly 5-10...

https://www.coast-bookmarks.win/for-a-practical-bedroom-setup-your-bedside-table-should-sit-level-with-the-top

For the most comfortable setup, aim for your bedside table to sit roughly 5-10 cm below the top of your mattress. This makes it easy to reach your phone or a glass of water without straining your arm