We purchased the Nook Pebble mattress and were very happy with the quality of the mattress itself. Unfortunately, since the mattress is heavy, it dips down in the middle when using a spring based crib. We had to put wood planks under the mattress since it was "droopy" in the crib we had purchased(with the springs as the base). For the price, we just expected the mattress to be a bit more supportive(of itself) and not need the extra support underneath. I see the exact same crib we purchased on display with a 'regular' baby crib mattress, and it appears that other popular/standard brands do not have this issue. It's not the biggest deal- but just surprised that a purchase this expensive would have any flaw. It was easily fixed, but will know for sure how effective the mattress is once the baby actually starts to sleep in the crib! Excited to use- but wanted to share this with perspective buyers!