Straw, without a doubt, is the preferred mulch; but, quite frankly, anything would work. Also, since they're shredded, you eliminate much of the danger of their matting down and smothering your garlic. I wouldn't worry about the ph affecting this year's garlic. They are acidic and great for blueberries over time, but one year's addition of them won't be that noticeable. They are great soil builders, IMO.

Brook

I wouldn't worry about using oak leaves as a mulch. If you are concerned, just apply a light dusting of pulverized limestone on the top of soil before laying down the leaves. That way any acid generated from decomposition at the soil surface will be mostly neutralized. If you till the leaves in next, best to add more limestone.

BTW, my best garlic bed a couple of years ago with the largest bulbs tested at 5.85 pH.

TomNJ

I used live oak leaves on my garlic last year that I hoovered up with my bagging mower - no problem. Dried leaves are a 'brown' compost, which means it requires nitrogen to break down, so if you use only leaves you will have to bump up your fertilizer a corresponding amount.