Seems that this is a highly personal issue. I have yet to experience a longhaul flight where I did not shiver and feel terribly cold using a blanket plus a sweater to keep somewhat comfortable and warm. FWIW it would suggest to use the "onion" model: Wear several layers of light comfortable clothing that can be removed or added easily so that you have a light sweater and long trousers in FRA while redressing for California (and change into short pants in the airplane restroom). Though wet and cool SFO can be quite a bit colder than FRA, especially in summer, so short pants might be more useful in FRA