Your residency actually changed when you permanently moved to Florida. Although it is easier to prove if you have a FL driver's license, etc., the IRS considers when you moved to FL to be when your residency changed. For this year, you should file a part-year resident Michigan tax return. You can find instructions on how to do that below:
Next year, you will not file a Michigan state income tax return (unless you receive Michigan based income like rental properties, etc.) and since Florida doesn't have income tax, you will not be required to file a Florida return.
https://ttlc.intuit.com/replies/3302008
