In every small village of Amalfi coast you can find a small free beach.
Normally the coast change between villages, in Amalfi you can find beach with pebbles.... in Maiori can find a sand ...
I suggest to swim in Amalfi or Atrani where the free beaches are very clean, the last time in Maiori was a little dirty.
For me the last beach close the park and port of Amalfi is comfortable...
