YouTube Focus

Nothing under the video you are watching, and no autoplay into another one. For Safari on iPhone with the free Userscripts extension.

Install YouTube Focus
  1. Tap the red button above. Safari shows the script as text.
  2. Tap the AA (or puzzle piece) in the address bar, then tap Userscripts.
  3. Tap Install in the popup that appears.
  4. Open m.youtube.com in Safari and play any video. The space under it should be empty.