[jeff st4s]

Before you all go no way.
BMW do some good if not expensive gear, they did do a body warmer shape liner that has inflateable sections, you could add remove air easily to help regulate your body core temperature, this may give you alternative ideas.
I used to have a Hein Gerricke master whatever it was numbered, in winter rode at 6/7 in the morning rain or shine and even in the snow (only a bit though) I rode that with the lining in and only a thin long sleeve top under it, no problems.