A flannelette sheet? I've only just taken the flanny sheets off DD's cot, she has a grobag which I just bought for her that I've been putting her in at night (she wriggles around so much at night, the last few mornings she has been sideways right down the bottom of the cot!). During the day I just tuck a sheet over her bottom half, so have just started using a summer cotton sheet instead of a flanny sheet. Folded in half they are quite warm.