The golden rule for bedside tables is keeping the top surface within 5 to 10 cm...

https://www.acid-bookmarks.win/to-get-the-perfect-bedside-table-height-aim-for-your-nightstand-to-sit-roughly

The golden rule for bedside tables is keeping the top surface within 5 to 10 cm below your mattress top. This makes reaching for your phone or a glass of water effortless while you are in bed