Maria is a good host. She is to the point and very responsive. She answered all my questions and made travel arrangements for us from the airport even though she was away for the winter. I especially appreciated that she always responds even just to say "your welcome" or "enjoy," so I know she got my message. The place was super clean on arrival, and she had a lovely cleaner come every day, mid-day, to tidy up, clean floors, clean the bathroom, and empty the trash.
If you want the most idealistic Santorini experience, Casa Sofia is it. We stayed in the apartment (note the pictures show a studio and an apartment). You can send a postcard home and circle the blue door that is a part of your cave house (it's the bathroom door). The cave house itself was so cozy, but still spacious, and beautiful on the inside. We loved the two couch/mattresses in the living room and the kitchen window view. Every morning was bliss looking out on the caldera from our roomy balcony, where the sun goes across the whole sky from morning to evening. It's one of the best balconies compared to others I saw. It's far enough down the cliffside off the marble way that you have more privacy from wandering tourists (you get a nice little workout). The iconic sunset viewpoint is just a few minutes walk away, or you can scale some nearby stairs just east of the house to get high enough to see the sunset fully. You can't see the sun sink into the ocean from Casa Sofia, but this is a good thing, it's fun to walk to the sunset every night, and return home to privacy. We visited in January, there were hardly any tourists, just enough was open (couple restaurants, couple stores, and the Atlantis bookshop), and the island was magic. Even with the construction they do in the winter to upkeep everything, it didn't distract from the beauty of the empty town. I had never felt more relaxed. It's easy to walk to Drossos and rent a car and drive all over the island for a couple days to see the rest of it, don't miss Akrotiri and Ancient Thera.
My advice for those who stay at Casa Sofia: Taking a bath is better, watch the stairs when you go outside to use the bathroom at night (the bathroom is separate, but it is nice to be reminded of where you are at 2 am), the mattress is a little hard so if that is a problem I would ask Maria first if she has added some padding to it, and lastly, pack lightly so you don't kill yourself or the nice porter that helps guide you down the many steps to the house (we had osprey backpacks, perfect).