I am definitely more familiar with Sardinia, Tuscany and Lazio.
I'll start by telling you that in Sardinia there are kilometres of unspoilt free beaches where there are few people even in August, which is good. I prefer South Sardinia because it is the wildest, the nature is unashamedly beautiful.
If you happen to go there, there are corners that are as evocative as they are peaceful.
Scivu beach is my favourite, then there are the white dunes of Porto Pino, Porto Paglia, or even Porto Giunco in the south-east, near Villasimius, where there is practically a forest of eucalyptus trees, a very long coastline of light-coloured sand and a pond with pink flamingos that have chosen it as their habitat.
But there are many more!