I have a temporary plan with a private driver from Naples to Matera, so if you are looking for same,, from Monopoli to Sorrento, this Sorrento-based company has excellent reviews and have been prompt in communicating with me, in English:
https://www.aldolimos.com
I've also found that our hotels, in recent years, have been wonderful in recommending drivers.
Yes, Matera makes the perfect stopping point between the Pugliese coast and Sorrento. We've been several times and will return in May (between stays in Naples and in Puglia) so I am happy to recommend hotels and restaurants in Matera and in the parts of Puglia that I know fairly well. One of the most memorable hotels stays I've had in Italy (and in all of Europe) was in Matera, at the SEXTANTIO CIVITA. Astoundingly great, and certainly unique.
The problem with some travel agents is that their visits ("fam stays") to a destination have very often been by invitation from a particular hotel. So they are going to recommend that hotel to you. And they would have had experience being driven around by the hotel, and dining either at the hotel or at restaurants recommended but he hotel. Their time, on working/scouting trips is usually limited and they will not have the free time to wander around and discover places not on their set itinerary. Nor will most have experience of having taken public transportation.
There are many exceptions, of course. I am with the others here who do not think you ought to use an agent and, in fact, I will go further and say that using an agent might be a negative. So if you do decide to use one, choose a travel planner with a speciality in southern Italy. Look at Condé Nast's annual lists of recommended agents, for example.
Having an agent based in italy would not necessarily be a positive. And be aware that these experienced travel planner will charge you a daily fee, or require you to spend a daily minimum that can reach upwards of the many hundreds, Into the thousands of euro if you choose the luxury hotels that the planner is likely to recommend. You might think I am exaggerating with the "thousands,' but take a look at the recent prices for the luxury hotels in Sorrento, the Amalfi Coast, and Puglia....I was shocked myself!!
You are planning to go in May this year, and I think you need to begin booking hotels very soon if you are angling for well-reviewed properties. Many are likely to be booked out already for your dates. Example: We are returning to a favorite masseria hotel in Puglia in May; when I booked last November, many dates were completely booked for the lower-priced room categories.
Anyway, sorry for the long ramble..feel free to ask questions..this is great bunch that can probably help you more than any random travel agent! And we don't work on commission.