congratulations!! Be really really careful using blankets in with new pups. I have seen pups get tangled up in blankets and smother before. I always use carpet. As it gets soiled or wet, I just replace it with a new piece of carpet.
I have raised litters ranging from Chihuahuas to Bouvier Des Flanders. I always used large carpet squares under the whelping box. My whelping box was made of 2x4's standing up on their edge, and then I screwed another 2x4 horizontally to the top edge to make a rail that pups could go under to...