ISO the best and cheapest ways to gain guardianship of a loved one with dementia.

Location: Florida

Fairly simple one this time, I think. My old man has fairly severe dementia and ALS and can no longer handle his affairs. He is cooperative with me and agrees I need to take things over but a notary won’t allow him to sign a pose of attorney given his mental state. What is the simplest way to achieve complete guardianship so that I can approve home renovations, go to the bank for him, etc?