At LOs 9 month check-up this morning, our pediatrician suggested no longer using the sleep sack so that LO can get more practice pulling up to stand (I haven't ever found her standing up in her crib at the railing). Our apt. is a bit cool at night and I'm concerned that she'll get too chilly and she also sleeps much better with the sack. Does anyone have experience with this or advice? I don't want to unintentionally hamper a milestone but until spring really comes to New England, I want to make sure she's cozy and warm.