请问 这个 crib mattress 怎么样?# NextGeneration - 我爱宝宝l*e2010-08-29 07:081 楼http://www.amazon.com/Serta-Nightstar-Extra-Firm-Mattress/dp/B000S9A37I/ref=sr_1_1?ie=UTF8&s=baby-products&qid=1283114634&sr=8-1-spell有姐妹买过这款的吗,是extra firm, 会不会太硬?谢谢