Alex's place is just as described - a cool, spacious-feeling loft in a perfect central location within an easy stroll to our favorite neighborhoods (Montmartre, Marais, the Latin Quarter) and an easy Uber or Metro ride to L'Opera, the museums and the less touristy gem of the neighborhood around the Buttes Chaumont park. The neighborhood around the loft is fabulous: lots of good cafes, bread, fruits and vegetables and a lively night scene bustling with young Parisians and (aside from us!) few tourists.
A few recommendations: Le Martel is a wonderful little restaurant across the street run by a guy who takes justifiable pride in his couscous and other dishes; Le Napoleon is a fun, rustic dive cafe with a blue collar vibe that's a great place to watch the parade of humanity; and check out the Basin D'Eau Douce where you can rent a small electric boat for a few hours to ply the canal stretching across northeastern Paris and a little beyond.
Other travelers have mentioned the low ceiling in the kitchen and bathroom; I'm 6-2 and those didn't bother me at all. But the ceiling beam stretching across the entrance to the bedrooms was a problem for me, especially when I needed to get up in the dark to go downstairs (via the tight spiral staircase) to the bathroom or kitchen. I took to wearing a hat to protect my head, but perhaps the host could put a little padding there :) Speaking of the host, Alex was congenial, super responsive and has built the place with a eye for design. It was also super clean and, due to the courtyard between it and the street, surprisingly quiet.