Not sure how to pick a mattress or what makes a good one, but this one is light as expected (I can lift at 32 weeks pregnant) and it fit in the crib I ordered - Newbury 4-in-1 Convertible Crib.  It arrived quickly and seems to be comfortable (but how can you tell?!??!).  Standard sheets from Pottery Barn fit it and it doesn't seem to make too much noise for when a toddler will be rolling around on it later.