My mother and I stayed at Julia's apartment for a week. Julia is lovely and communicative, we also appreciated her flexibility with our early check in. The apartment is perfectly located on the south side of Montmartre, first floor (there was one flight of stairs, approx 10-15 stairs from ground floor to apt, it was not a huge issue carrying the suitcases up and down, as long as you have one person who is able to briefly lift them). The apartment is central and therefore you may experience some noise at night. There's a pull-out bed in the living room and one double bed in the bedroom, both comfortable but I probably wouldn't recommend the livingroom one for over a few days' stay. Everything was clean and Julia was sweet to leave a complimentary bottle of wine for us.
I would advise future guests not to open the windows too much because there are no screens and bugs do come in, mainly fruit flies that can really be bothersome at night (they buzzed in my ear and woke me up!). You can use the AC which has a cool/heat/fan setting to circulate air instead. For winter months, there's an additional radiator in the bedroom for extra heat!
At one point, we had a strange hot-water issue where it went instantly cold, but it was clearly a fluke, and Julia came by the next day to make sure the system was ok.
Overall this was a wonderful stay, great value and we appreciate Julia's hospitality. Thank you for making our first time in Paris a positive experience that we'd fondly look back on!