How difficult is it to find a job in Silicon Valley from an outsider?

Cost of living in Silicon Valley is so high that you would barely be able to afford a small apartment there, despite what sounds like a "high" salary. If you hold at least a master's degree plus 3-5 yrs of experience, and can find an open position with a qualified employer, expect to compete with 100-1000 applicants for any job which might offer prospects for a temporary employment visa. Not an immigration visa! Maximum 3 years, with the possibility of extension for up to 3 more years, at the employer's option, not yours.

The best way to do this would be to work for a company in Italy that has US operations.  Once in the company, doing good, seek opportunities and transfers to the USA.   If you are selected, the company would do all of the visa, etc. and you would make a move as an employee.  You also might find a great job in a really nice part of Italy, which would be better than California.  Your current company may think poorly of you by your wholesale job search and ruin your opportunities with that company.  And, it is not going to work unless you are obviously exceptionally qualified, which you say that you are not.  If not, you need the "introduction" connection through your current job and company.