We stayed at Savash apartment for a weekend and really liked it.
The flat is very well located, in a quiet neighborhood next to the Galata tower. There is a heater inside and one can control the temperature in the flat. A good cafe Arada with a great breakfast/lunch is nearby, small shops to buy grocery if required.
The check-in and check-out are easy and smooth. And there is a local guy nearby who can arrange a taxi or help with other issues.