I'm finishing up my last night here at Le Petit Cosy Hotel in the 12th arrondissement, and thought I'd put in a word for it as a nice option. I admit to being initially attracted to the name, and can say it lives up to it!
The closest Metro is Picpus, though Nation is an easy walk as well. This could come in handy for those wanting to arrive in Paris via RER. If you have luggage, you can make an easy change at Châtelet to RER A, get off at Nation, and take advantage of their elevator, then do a quick walk, easily less than 10 minutes, to the hotel. To get off at Picpus you would need to navigate stairs with luggage.
The neighborhood is not very touristic, but has simple (though sometimes long) connections to major destinations. You can get easily to the Coulée Verte walkway, and I found myself heading to Bercy Village more than once for shopping, a movie, and taking in a different "vibe" in Paris. It struck me as a nice place for anyone seeking a more local feel.
Rooms are clean and well-organized to use the small (cosy!) spaces well. The decor is modern and attractive, leaning more on the hip side with pretty accent walls. Reception is friendly, with I believe possibly the manager or owner being an American expat who was frequently present. Everyone was responsive and pleasant, with one employee even carrying my bags upstairs without me asking for help. That being said, they are narrow stairs, and could be quite a few depending on where your room is; no elevator if that matters to you! I believe I paid around 125 euros / night for a single occupancy room.
You can include breakfast in the attached cafe / restaurant for a fee; I did not, so I can't speak to it. I did eat dinner there one night and found it to be a pleasant, nicely decorated spot with appropriate pricing and again, friendly service (I had a laugh listening to a waiter imitate Bob Dylan to himself as "Like A Rolling Stone" was playing).