I also struggle with acne and constant oily skin. What I have found that helps is cerave hydrating lotion spf 30 matte finish. It moisturizes, protects, doesn't clog your pores, and it doesn't look like an oil pit on your face!! I love it.

Regarding your initial question, I have seen many dermatologists who state that no matter where you are you are always going to be receiving UV exposure. Inside or outside doesn't matter. I just use it in the morning and then on sunny days reapply in the afternoon.