We had a great stay at the Casa da Suite Cometa. The apartment is about 10 min walk from Castello Sforza, less than 30 min from the Duomo. The sofa bed in the living room sleeps very well (as do the 'normal' beds), the air condition works (which was great since it was really hot), the kitchen has all the basics to cook some simple food. A supermercato is around the corner, what else do you need?