I love the Gerber Sleep N Plays - we dress our newborn in them pretty much all the time, since they're just so easy. The fabric weight is just right - she's all covered up but since the fabric is lightweight, she doesn't get too warm (our baby is only 3 weeks old so we do spend most of our time indoors - when we take her for evening walks in the stroller or out to a store, we just add a blanket over the car seat straps to keep her warm enough).
The patterns on this yellow set is adorable, gender-neutral and age appropriate.
The only reason I gave it 4 stars instead of 5 is the sizing seems a little small to me (though I don't yet have enough experience with baby sizing, so maybe I'm off.) We bought the 0-3 months size, thinking it would just be very big on the baby for a while and we'd get more use out of it. It was huge for a few days, but she quickly filled it out, and I don't know that we'll get even another month out of it. My baby is currently 3 weeks old and weighs about 9.5 lbs., so I am a little surprised at how quickly she seems to be outgrowing it. You might want to order a size up.