Welcome
@Sunic68
There is a pretty new book just out....in Italian.....from Terre di Mezzo. Before this there was nothing for many years. Very fine maps if you like maps. Lots and lots of information (and a lot of photographs too which add to the weight!). I did the route before it came out but I would have used it if I could if you see what I mean.
Da Roma a Santa Maria di Leuca: un cammino spettacolare tra antiche vie consolari, aree archeologiche e naturalistiche, castelli e abbazie, e orizzonti sconfinati dove terra cielo e mare si uniscono.
www.terre.it
Waymarking in 2018, when I walked from Rome to Brindisi, was patchy, depending on local volunteers. I think there is a fair bit of enthusiasm along the way and marking is improving. I walked the final stretch from Brindisi to Santa Maria just before Christmas last year.
There is a Cammino di Salento - slightly different route from Lecce to the finish. But if nothing else buying the credenziale in Lecce gives you a great discount in a couple of hotels - no religious hostels down that way. And a big discount on a meal in the main hotel in Santa Maria - which is quite a small reserved place out of season. There is a very very good hostel in Lecce just south of city centre.
www.camminodelsalento.it
I am not aware of a book in English.