The plains biome is your original starting point, but you really need to move westwards from there. At these coordinates -1179 68 373 you will find your first igloo hidden behind a small patch of forest trees. This igloo has a secret room underneath the floor, so go ahead and grab that golden apple.
The other igloo is located a bit to the south at -1199 69 752, and it's kind of half-buried under the layer of snow. This one also has a basement below with another cool chest holding: