I feel your pain, I live in Denmark right now and the long winter nights can take their toll on your Vitamin levels. I always supplement year-round with Vitamin D3 ( the most absorbable form) 2,000IU a day.
Food-wise I favour egg yolks and fatty fish, so Omelettes and Salmon are my go-to dishes.
North latitude solidarity! I don't live that far currently, but I've been there.
Any recommendations for vegetarians, too?
Yeah, Soy milk and soy-derived products can provide a decent amount. I also like to incorporate mushrooms into my diet, that have a range of minerals including vitamin D.