@Alice ************
, you won't be getting a "visa on arrival" because italians get a 30 day visa exempt entry stamp instead.
Also make sure you go to the immigration office and cancel your current ED visa extension too.
Depending on the border you're entering thailand from you could be requested to show any or all of the 3-proof-ofz
proof of adequate funds (10K baht cash on visa exempt entries)
proof of a hotel booking or confirmed lodging
proof of onward travel in 30 days
You most likely won't be asked to show any of those but be prepared just in case.
You will have no problem getting another 30 day visa exempt entry when you come back to thailand from Bali