My son slept his first seven months, until he was just too big for it, in a car seat because he slept all night long by two months. As for the comfort issue in a play pen, babies don't give a flying flip. She would not sleep if she ws uncomfortable. The only thing is when she does move from a play pen to a bed or crib, it will probably take a much longer time for her to adjust. Once we started putting my son in a crib to sleep, he stopped sleeping through the night. He is 3 now, but until he was over two, he wouldn't sleep in a bed all night long. Thank goodness those days are behind me. My daughter slept in a crib from the start, and she was just fine until she decided she wanted to sleep in a bed like her big brother. So, my only warning to you would be that she may get so used to the play pen that she will want to sleep there until she is big enough to want to be in a big girl bed. Oh, besides the fact that if you ever want to use that as a play area when she starts getting mobile and she only knows that as her bed, she may not take too kindly to being put "to bed" when she is wide awake. This is more lengthy than I intended, but I hope it helped.