As far as I know there is not a good book/guide on Italian battlefields and unfortunatly it is hard to find a battlefield that is preserved as you can find in UK or USA (I mean with info point etc).
Most of the battle fought in Italy were in the North that is the most industralized area of the country, so many buildgings.
There are anyway many "preserved" battlefield as in countryside.
Let's start with the Great Italian Wars as you mentioned Bicocca. Bicocca is part of Milan, so absolutely nothing see.
Marignano is now called Melegnano. From Milan if you go south you pass by. Actually the battle was fought not in Melegnano but between San Giuliano and Zivido.
It is hard to have a general view of the battlefield but there are some places that witnessed the events.
For example the remains of the castle of Brivio picture
were hundred of Swiss took repair after the battle and were burnt inside.
Then we have Pavia that is a nice town on its own so worth the visit. If you have the Osprey campaign on this battle you have a good guide. Still not ieasy to have a general view due to the complexity of the battle.
Still in the are is Agnadello. The battlefield is abiut the same as it was. I live just few miles away and I can do a guide if you want (you can write me at dadiepiombo AT libero DOT it)
Worth a visit is Fornovo. From the A1 highway (the main route that connects Milan with Rome and Naples) if you just before Parma take the A15 highway (towards La Spezia) you will reach in a few miles the Taro river and can have a clear idea of the battlefield.
At Ravenna you will get a Byzantine flavour more than Italian Wars.
In Tuscany there are some battlefield related to the Communal warfare and these are Campaldino (go to Poppi link Montaperti (near Siena link and Colle Val d'Elsa (worth a visit for the typical village picture )
experiments at 11x.