My lovely apartment is perfect for two but accommodates up to three people. It is located in the beautiful prestigious Töölö neighborhood, only 10min from city center by tram (10, 4, 2). Neighborhood is filled with great restaurants (LieMi, Linko pizzabar), shops (daily groceries + boutiques), and next to my place there is the Helsinki Ice Hall where you can go to see local ice-hockey games.
Calm area still so close to the center. Easy access to everywhere by public transportation. Good places to eat and have a coffee.
You can take direct bus 415 to the Helsinki-Vantaa airport (stop is 350m away and called kansaneläkelaitos).
Trams 4, 10, 2 (stop is next to my home 100m) take you to the city center.