You absolutely can, especially if you're a casual resort skier who prioritizes comfort over peak performance. A regular fit base layer gives you a bit of breathing room—it's comfortable, easy to pull on, and more forgiving if you're between sizes or just don't like that skin-tight feel.
The trade-off is moisture management. Base layers work best when they're in direct contact with your skin to wick sweat away efficiently. A regular fit leaves small air gaps, which means sweat can hang around longer and leave you feeling clammy—especially on cold lift rides after a hard run.
Regular fit shines in warmer conditions, on milder spring days, or if you tend to run hot and don't sweat much. If you go this route, just avoid sizing up even further, and consider a merino wool blend, which handles moisture and odor better than most synthetics when the fit isn't optimal.