Mitsuko's apartment is perfect for 2-3 travellers. We stayed for 7 nights and found it very easy to explore tokyo. The closest station is 5 minutes on foot, and the station is 2 stops from Shinjuku. The area itself is really nice too, with many bars, shops and cafes around. We stayed in hot and humid June, and the air conditioning in the apartment really helped beat the heat!
Mitsuko was really nice and accommodating, although we didn't see her very much. She brought around cakes and let us check in quite late.