As mentioned, South Fl., over and above what it already has become, gets very crowded with winter snowbirds because of the tropical weather. You can always identify the transplants during the winter. I lived in Key West back in the 60s, having moved there from my native Jax., FL. in Oct of '63. I was one of only a few in high school who made it through the winter in short sleeved shirts and hit the beach in a bathing suit. '64 was a different story. I dressed like the locals as my blood thinned out. Navy kids moving in after I did, made it through the winters in much the same way while stationed there... lol. It's all relative... what you become accustomed to.
As a working full timer, I travel without reservations (zip, zero) and usually winter in north and central FL. It's nice to reside in the few remaining vestiges of "Old Florida" where life is laid back, cost is more reasonable and the pace is slow. This year, as a walk-up, I spent Nov and Dec on the "Forgotten Coast" at a city park, FHUs @ $15/night and I'm currently near the state capital in a commercial park, full services @ $485/mo while visiting family. You'll find winters in the sub-tropical parts of the state to be quite mild relative to temps in SD. Good luck and travel safe.