If you want to avoid big Venice crowds then you should definitely consider your stay at Castello area or more precisely Giardini Biennale. Elena's place was impeccable and felt like "home away from home". Clean and nicely decorated with many amenities. Since there were 4 of us and we stayed there at the beginning of July, you can only imagine our sweaty clothes. There is a washing machine in the unit, ironing board and iron, and we never had to feel like "wrinkled" tourists.
It is within a walking distance to St. Mark's, just few minutes walk to the Arsenal and Giardini Biennale, two min walk to the water transportation, etc. There is a great grocery store, pharmacy, fruits/vegetables stand, and numerous coffee shops and restaurants. If you are not traveling to Venice but you know someone who is, please recommend this place. Worth it every penny.
Elena and Brigitte are very fine ladies and easy to communicate. Highly recommended.