Very quiet and comfortable. We had a wonderful sleep in the flat, although the lower room tends to be a bit cold if the heating is turned off during the night. The kitchen is well equipped for basic cooking and there are several supermarkets (Sainsbury's, M&S's, Iceland) and fruit/vegetable + fish shops within 5-minute walking distance. You do not need to bring slippers as the whole flat has super fluffy and warm carpets everywhere, including the staircase.
Kathy is a wonderful host, responding quickly to any messages and willing to adjust check-in time.
I know where I am staying when next time in London. ;-)