If you are planting an Avocado seed, you are almost certainly giving up the thought of having the tree produce good fruit. It would not produce fruit for many years anyway. Avocado trees for fruit have a good cultivar grafted to a hardy rootstock. This helps them produce fruit much faster.

Trying to grow an Avocado in a container is a separate challenge. Even if you bought a good variety and kept it in a good climate for Avocados, the chances of making it happy enough to produce good fruit is very small.

If you live in an Avocado climate, just choose one of the smaller varieties. Wertz is small. Reed is fabulous tasting and not much larger. Reed grows mostly upright so does not spread real wide like most Avocado varieties. You could keep it to around 10' wide pretty easily.

good advice above....my favorite dwarf avo is the "Holiday". It has fantastic fruit (large) and the tree stays pretty small. Of the 16 varieties I have...it is one of my best eaters. That would be my choice.