Age 89 with no relatives or friends, in good health & finances. What springing medical & financial guardianship would be possible in Florida?

I used to live in Florida and believe it is possible. However, laws change, and you need someone to advocate for you as you move forward to name someone. Find an eldercare attorney with an office nearby. Call and ask if they offer a free consultation. They may be able answer all your questions.

As an aside, when I lived there I knew of an elderly woman with your situation. Her bank, which had managed her income for years, was her guardian (I think that's what the relationship was). She stayed in her home for many years with home caregivers managed by the bank. People at the bank kept her checkbook for her. Some retirees from the bank were paid to come and read to her or spend time with her. She lived to almost 100.

You will need to consult with an Elder Law Attorney in your own area. You will find them listed on your computer. This site is just caregivers asking and answering questions about hands on care, but for medical and financial and legal guidance you really need an expert in that field.

I wish you good luck finding someone who can guide you. You might try looking up Licensed Fiduciaries, as well, or asking an attorney to recommend a Fiduciary they work with through the court systems.