Yeah, technically it requires diacritical marks, but unlike French they are only written explicitly when they fall on the final letter of a word. Italian only has seven vowels, so these are the only common ones: è é ì ó ò ù à.

What I would do is this:

- Replace them with a single quote -> E' instead of È or É and so on.

- Ignore all uncommon marks.

In most contexts, it is perfectly acceptable to do that. A native speaker would understand without giving it a second thought or considering it impolite. I write emails to my boss like that.

If I had to make something meant for the public (say a UI, or a document), then I'd switch to the Italian layout for that purpose only and then go back to the US one.

Not for Italian, but I use a US keyboard layout with the addition of German umlauts behind right alt + letters (as well as right alt + ' and right alt + ` being dead keys to put accents on letters for foreign words). I find this much better than the standard German layout which puts all of @{[]}\~ behind right alt - and most of them on the right side of the keyboard too so you have to akwardly hit the right alt + combo with a single hand.