便宜的普通海绵的可以去Walmart或Target买: http://www.walmart.com/ip/Beautyrest-Bed-Bug-Resistant-Memory-Foam-Topper/19589823
贵的记忆海绵的可以等Costco有sals的时候买。一般来讲,越厚的越贵:http://www.costco.com/NovaForm%C2%AE-Pure-Comfort%E2%84%A2-Memory-Foam-Mattress-Topper.product.11765557.html