Kate, not sure if you'll see this message. I tried to see if you had an email connection from your member page but I didnt' see one. I have started 2 apple espalier trees, Freedom and Liberty. I am in north MS however, and not sure if they would grow there, becoz apples need some cold.
I would check with the county agent, master gardeners, or whatever university is close to you that might have an ag program (horticulture or agricultural extension service). You might even google espalier+fruit+florida and see what comes up. There are regular, semi-dwarf, and dwarf varieties of many apple and pear and other fruit trees. You would probably want the dwarf varieties. They are harder to find at stores or nurseries but can be ordered online from various growers. I think citrus would work for you, lemon, orange, satsuma? I think fig would work, I have a fig I am deciding if I will espalier or let grow large. You can keep it a certain size by the pruning process. Good luck.
Laurie