I stayed at Katarinas house for one month. She is a charming and clever host, very communicative and eager to solve your small and big problems - and Katarina answers your mail immediately.
The room has a small kitchen, nice bathroom and good terrasse, the room is very clean and comfortable. The house is situated close to Apollonia, the mail city on Sifnos. The view from the house is to the field and the street. The bus stop is right outside the house, it means that you can go by bus to the beach(es).
I recommend you to book at Katarina - she lives with her family and the atmosphere is very warm. You will not regret your choice.