Greece tips - quiet, fewer tourists?

[SeismicSalad]

We mostly go on holiday to the Alentejo region of Portugal, where we love the beautiful beaches, relaxed pace of life and not so many tourists (much, much quieter than the Algarve). But it’s time for a change! We were thinking of Greece but there are so many options… Can anyone suggest equivalent kind of places? We don’t have kids.

I think the Pelepponese is generally quieter and has good beaches. Never been but the peninsulas south of Kalamata look lovely.
Alonissos and Amorgos are two islands that I know to be on the more peaceful side with low key tourism.