I know from reading my trusty Baby Bargains that a perfect fit is needed. How did you make sure you got the right fit? Measure once assembled? Go with the mattress the seller recommended?
I just ordered the Olivia set from JCP, and there is one mattress linked, but nothing promising it's the right size and I'm not sure how to know. The sizes listed with external measurements, I'd assume (to make sure the furniture fits in the room).
Re: RDQ: How did you decide on a good fit for crib mattress?