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

https://www.bookmarks4all.win/for-the-most-comfortable-reach-your-bedside-table-should-ideally-sit-5-10-cm

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