M's place was just what we needed when my sister and I stayed in Tokyo for a night. Although the listing says it's just a private room, it's actually the whole studio apartment, so it's very private. The room is small, but comfortably fits 2 beds. We loved the bookshelf full of manga in the room as well! The balcony was also great. M provided us with towels and toothbrushes as well as an array of other amenities in the bathroom. The water takes a few minutes to heat up, but aside from that, it was a perfect place to crash for the night. M's place is a 2 minute walk to the Keikyu-Kamata station, which has a line that goes straight to the Haneda airport (only an 8 minute ride!). The place is also a 10 minute walk to Kamata station, which is a much larger station that connects to many lines. Right around the corner is a nice shrine with beautiful cherry blossoms, as well as a 7-Eleven. I would highly recommend staying here if you're just looking for a place to spend the night.
One warning - (SENSITIVE CONTENTS HIDDEN) Maps has a hard time finding the address to this place. Follow the map that Airbnb provides instead!