I highly recommend layering tights/pantyhose. I used to wear up to 6 pairs at a time and only a very light (shirt weight) pair of trousers (think pj bottoms style) whilst out and about in the snow here (UK - so coldest around -5degrees Celsius) and never ever felt cold. I also think vests (the undergarment not waistcoat type) are worth their weight in gold. I frequently use light summer weight simple elasticated skirts under warmer winter weight ones. Works well and saves on extra cost. Full length petticoats (the kind that look a little like summer dresses.) are brilliant too. If you can possible afford silk it is well worth it for thermal qualities and not being too bulky.
All of mine I make from a basic elasticated waist model that sounds very similar to what you make.