Been there, too! I use Neutrogena Healthy Defense, a tinted moisturizer with SPF 30. It's light, non-greasy, promises not to clog pores, but gives some light coverage to even out skin tone. I know Neutrogena also makes an oil-free tinted moisturizer with SPF 15, but I haven't tried it.
I also prefer the natural look but need some coverage for acne, and my favorite cosmetic is my medicated cover stick. The one I use is made by Clean & Clear; it's an effective concealer that brings red pimples back to skin tone without looking "make-uppy," and best of all, it's a salacylic acid acne medication, so it dries and clears while it's hiding the pimples, rather than making things worse.
Hope you enjoy your trip - I know exactly what you're going through. My adult acne makes me so self-conscious that I sometimes insist on dimming the lights at night, claiming it bothers my eyes, when actually I just want to try to hide my blemishes - and I've been married more than 20 years!