I keep mine in the kitchen or living room. It really doesn't matter if the rooms are a bit cool, as long as the temp is stable. You don't want to keep the bator near areas where cold air is going to flow over the bator like near an outside door or open windows. If it is always about the same cool temp, the bator will hold a good temp. It is when there is cold air always blowing around the bator and it can't keep the proper temp.
If your sewing room has quiet air in it and it remains fairly stable, this will be a good place to incubate.
If your sewing room has quiet air in it and it remains fairly stable, this will be a good place to incubate.