Light is the strongest signal your body clock takes, which makes blackout the cheapest lever you have. Curtains solve the whole-room problem in a way a mask cannot: you move in your sleep, masks shift, and a room that is bright at 11 a.m. will wake you regardless of what is on your face. A mask solves the problem curtains cannot — the edge gap around a rod-pocket panel, and every bedroom that is not yours.
Owning both is normal and neither is expensive. If you have to sequence it, curtains first when you own or can mount hardware, mask first when you rent, travel, or sleep somewhere different between stretches. Nothing on this page is medical advice: if daytime sleep is persistently broken, that is a conversation for your own clinician, and shift work sleep disorder is a real diagnosis with real management.