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

https://www.bust-bookmark.win/aim-for-your-bedside-table-to-sit-5-to-10-cm-below-the-top-of-your-mattress

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