Since it's only one tree why don't you get a multi-budded tree and have a few varieties on it. Look for some of Dave Wilsons trees, they are sold all over the bay area, from the big box stores to Summer Winds to the little guys. You can get them off the internet as well. Santa Clara Master Gardeners recommend you plant the tree bare root, in the dormant season (Jan/Feb) and use native soil only, slightly mounded... Here is a link that might be useful: Dave Wilson Fruit Trees

I live in Danville, I have about 10 different types of trees. Most of my true tropical types (I got the seeds from India.) die over the winter but grow back. Nothing works for these, No matter how much I cover them, it seems just when I think, its warm and take the cover off, boom, the freeze comes and they are fried crisp over night. Some of my varieties (those purchased here locally) made it even through the freeze this year (2013). The one I particularly like is a type called lemon guava. These are small yellow fruits, that are very tasty. These made it just fine, fruiting all through the winter. Am thinking about building a small three sided greehouse for my trees.

And the likely reason the plants are sold in small sizes at the local nurseries is because they all have to go in a greenhouse during the winter, and can't be left outside. sort of a catch-22. Tropical trees growing in small containers are a lot more vulnerable to cold because there is no insulation to keep the roots from getting as cold as the outside air. It's not as practical for the nursery to store so many big sized plants in their limited inside space. You are indeed right, that is probably the reason gardeners in sub-cold climates have generally not had success with tropical fruits; young plants are more vulnerable and not able to tolerate the winters.

With most avocados, you need two plants (a type A and a type B) in order to produce fruit. This basically means they need cross pollination from another variety in order to set fruit. I am guessing you have a Hass avocado which is type A. Type B cultivars that can be used with this variety are Fuerte, Zutano, Bacon, Whitsell or StirPrize. Your pot seems awfully small. Any chance you have room for it in the ground? It probably would be much happier. If I were going to plant it, I would cut it right before it changes from the darker green color to the yellow green color (based on your picture). If you need to keep it in a pot, I would get a bigger one to put it in. A good book to reference is the Sunset Western Garden Book, which has quite a bit of detailed information regarding Avocados. Most libraries have this book, so it is worth checking it out.