John

Probably not. Are you alone or traveling alone? If there is such a thing in or near Florence, I guess it would be in a hi-end hotel. I have no way to know much better than you do. Check reviews of hotel on Trip advisor. Italy is probably a conservative catholic country; I read that people dress fancier than in the USA; Italians are probably more afraid of nudity than Germans or northern Europeans. If you are a single man who rarely manages to interact with women, like I am, you are unlikely to be that much happier seeing naked women in a sauna than without seeing naked women in a sauna.

Agree with previous post, if you are looking for casual coed nudity, Germany and Scandinavia are better bets than Italy.

Dario???? Roberto????

Haha, Zoe, I thought the same thing!!!

This is certainly one of the more unusual posts I've ever seen on the forum. I agree with the first reply in that this sort of thing is probably less likely in Italy than in Germany (although I've never checked).

I'd be afraid to appear at a nude spa in case someone calls out the harpoon squad.

John, you might want to change the title of this thread to more closely reflect your question.

I think nudity is an option at Gabrio Staff Olimpo spa on Via Tornabuoni, but I have never been inside.

There is also the Tropos spa and the Asmana near Campi, but I don't know if you can go naked or if you can go textile only.

Throughout Tuscany there are lots of spas, but no idea if you must go textile. I think the Adler permits or even requires nudity in the sauna, not sure about the pools area.
https://www.adler-thermae.com/en/?tao_campaign=c896yobo2o&gclid=CI327cjx19ICFUlNfgodYcYOKg
Petriolo and Saturnia have some naked people in the rivers but I don't remember at the actual resort. Those aren't close to Florence anyhow.

Overall I don't think there are like in Northern Europe.

Search the open internet for nude beaches in Tuscany. It looks like some exist. See if they sell sunscreen in italy.