I stayed one month in Riga, and chose Mira's place. The place is enough for a solo traveler that wants to visit the city. You have a kitchenette, a washing machine and it also has a desk, all in the same room. The toilet if outside the studio but I never had any problems as it was almost always free when I needed it.
Also, the neighborhood is quite close to the center so I never had the need to use public transportation.
About the shower, I got a membership in People Fitness (25€/mo) that is also available in Vilnus and Tallinn. It was actually the best choice as I got to start working out every day, so that's a win-win.
I'm super happy with my stay in Miras's place and the city in general. If you are a solo traveler, it's a great choice.