I don't suppose you have any video, or even still photographs, of your skiing? We'll really need a little more information before we can give you any specific suggestions.
In general, though, I'd suggest that it's not really about keeping your upper body facing down the hill. It's not about the upper body at all! It's about developing accurate movements of your legs and feet, from the hip sockets down, below a stable pelvis and upper body.
Many skiers habitually use their upper bodies to force their skis around, which causes all sorts of problems. One of the outcomes is that the shoulders will rarely face down the hill. But that's really just a symptom of the problem. If that's you, it's unlikely you'll solve the problem by just focusing on keeping your shoulders down the hill. You'll need to develop an alternative movement pattern, using your legs themselves, not your upper body, to turn your skis.
When you activate your legs, the need the throw your upper body around will diminish, and you won't have to worry about keeping it facing downhill. Accomplishing this change will be difficult without a good lesson, or several. But again, if you could start by providing some video, we might be able to zero on a solution for you to play with.