We did something similar a few year back. We flew to Rome, hired a car and spent the first week touring, staying at Sperlonga, Pompeii and Tivoli before settling down for a week in an apartment in Santa Maria de Castellabate, a lovely resort on the Cilento coast. We saw loads, including Ostia Antica, Pompeii, Ravello on the Amalfi coast, Hadrian's Villa, Paestum and more. The apartment we booked trough http://www.summerinitaly.com who have a good choice in the area.

Hi

Have you tried Cosmos Tourama - they specialsie in one week tours followed by a week stay

Good value

Their on line company is Archers Direct

Worth a look