7-10 Days Amalfi Coast

Ravello, above Amalfi, is a great place for a relaxing stay but it's far from beaches. I like Praiano, less hectic than Positano. If you can have two bases, Sorrento and somewhere on the Amalfi Coast would give you access to Capri, Pompei, Napoli and other towns.

And it does make a difference as to how long you need as to what you would like to do......you say you want to relax? What does that mean for y'all? If its laying on a beach, you can figure how many days you need, if its beach every other day, you can pick the sites that you want to visit and total them up......but here are things to see in the area...

Easily accessible from Sorrento (but not on the Amalfi Coast)
Herculaneum
Pompeii
Vesuvius
Ischia
Capri

Easily accessible from cities on the Amalfi Coast
Amalfi
Positano
Ravello
Vietri sul Mare
Salerno
Paestum
Capri

Also, I'm not a lay on the beach person, so I don't know which city has the best beaches, but maybe somebody else might chime in....

figure out what appeals the most to you and plan your days accordingly.....

If you get to Paestum, there are nice beaches there, a beautiful archeological zone with Greek temples, and mozzarella farms. There is a nice hotel/restaurant from which you can see the temples and there is an entrance to the archeological zone on the hotel's property (you don't need to be a guest to buy a ticket or have a drink on the patio).

Nobody calls the city of Naples relaxing, but if you're staying in the region for a week or more, it would be worthwhile to go into the city to see the Archeology museum. More than a week sounds like a bit much to me, but that partly depends on whether you have already fit in everything you want to see in Spain.