I can only but recommend Isabel and Mario's place! The room is on the other side of the backyard of their house, in a very quiet area. The space is very cozy and super clean! There is small kitchen and even a washing machine, and the bed is really comfortable. If you have light sleep, make sure to bring earplugs because the ventilation of the freezer can be noisy (I always use the and for me it was fine). The bathroom is separate, in another room facing the garden, but it's not a problem because it's always nice and warm in Valencia.
Communication went very well, even though they don't really speak English.
The house is basically in front of the beach and there are several bus lines stopping in front of it or nearby, so it's very easy to reach the city centre or the train station. The evening I arrived I had to take cab because of a terrible migraine, and the ride from the Sorolla station costed 12EUR. In the area there are also supermarkets and several places to eat.
My stay was certainly great and I hope to come back to Isabel and Mario's place if I return to València.