I have zero experience with growing in Florida, or any climate remotely like that. BUT ...
These guys say:
"The challenge with heirlooms is to find the right one for the right time and place. And since growing in Florida has enough special challenges, its best to do a little research and save yourself the head and heart ache of another small harvest. There are plenty of heirlooms that thrive in Florida's climate. Below there are over 100 heirloom seeds that have been tested by the University of Florida and proved themselves superior."
However, they have over 100 heirloom varieties, so they MIGHT be more like collectors or archivists than hungry gardeners looking for just one GOOD variety!
These other guys have "Florida" all over their home page, and publish a downloadable a "Florida planting schedule" that might be helpful until you get some successful crops to tell you "THAT was the right time to start them".
They seem to have such a small number of varieties, I'm guessing their selection of cultivars really is appropriate for Florida.
>> Well, after much trial and error
I've found that personally contacting seed vendors will sometimes put you in touch with a real expert. Since you've already tried and erred, you are their target audience.
By phone or email, put together 2-3 questions that show the expert that you've given it some thought, and motivate her or him to get involved. If they are like Baker Creek or Kitazawa Seeds or Botanical Interests, and you get lucky, they might enjoy going into detail with a customer who appreciates their expertise.
For example, mention varieties that you've tried and not gotten good harvests from. Or pick 2-3 varieties from their list that look maybe-good, and ask if they are suited to your particular micro-climate or growing method (rows, raised beds, containers).
Sebastian, FL is near Melbourne FL? Then I think your ag coop extension office is this one:
Cool, they have an "Ask An Agent" email address, and sugegst sending photos with questions!
County Fact Sheets with gardening guides:
But I'm not finding lists of cultivars recommended for the Florida climate ...
Suggested Varieties for Florida Gardens
Yayy! That should at least give you some suggestions to start with. Maybe you could pick several from each category, list those, and ask more-experienced FL gardeners what their results have been with those specific varieties, or what they personally prefer. It's often easier to reply to a specific question than a general one.
However, some of their suggestions are more detailed than others. When they list "varieties" of Chinese cabbage suited to Florida, they just list the general names for EVERY kind of Chinese cabbage AND all related varieties.
But they have lists of specific cultivars for several kinds of beans, cabbage, beets, broccoli, etc etc.
Cruising the thread titles in the Florida Gardening Forum didn't turn up any discussion of specific cultivars OR praiseworthy regionally-focused seed vendors.