Helena's place is great! Everything you want to see on both sides of the river is within an easy walk or tram ride (tram goes right by). We loved the big windows that overlook the river and let the breeze in, and every morning, we heard the carriage horses clip-clop by on their way to work. One of the most thoughtful touches is Helena provided a mobile hotspot, so we had wi-fi wherever we were in Prague.
There is a little market two blocks away that is open late; on the way, you'll pass a wonderfully friendly ex-pat bar, Bar No. 7, that serves Únětické Pivo beer for 25 korunas (about $1.10) at happy hour. We made it our local. Go down two doors farther to U Zpevacku for excellent Czech food.
Two minor drawbacks to be aware of: The street is noisy, between the tram lines and late-night revelers (singing while doing push-ups, one night). The breeze outweighed the noise for us, but you might want to bring earplugs. And the bed (which is comfy) is only about 12 inches off the ground, which my husband's aching knees noticed every time he got in or out. Neither would keep us from staying here again. We loved it.