If what you're looking at is called the Graco Pack 'N Play Playard with Bassinet, it should work perfectly (at least, that's what we have). I've been very pleased with this mattress that my new granddaughter uses when she visits. This fitted sheet works perfectly with it, also: Fitted Pack N Play Sheet in Traditional Neutral Print
I'm not sure what you mean by bassinet? The mattress fits in the bottom of the regular sized pack n' play pretty nicely. Just an FYI, I found it a bit flimsy still and not as firm as I thought it would be. You can fold it in half easily.
This mattress fit my Graco Pack 'N Play Travel Play Yard with Newborn Napper Station LX (Bermuda) perfectly, as if it was made for it. I highly recommend this product, it has not compressed and has remained firm after two months of the baby sleeping on it.
This mattress fits both of our Graco pack and play bassinet inserts well. One PnP is at least 4 years old, the other brand new. The mattress has held up pretty well even though our baby sleeps on it at night and for naps, and is huge and heavy (30" 25lbs). (She hasn't started to push up so she's still on the "top floor".)