Hi....I will be in 30 to 40F temps at night. I have a Hennessy Scout Zip, so far, plus a zero down bag and of course....proper clothing. Trying to find the right combination of lightweight items to keep me warm from the underside. What about bivvy blankets? I also own a thermarest pad that is 4.9R. What is the best option if I can't afford an underquilt right now? Even heard someone say that breathable hammock socks (I see a reasonably priced one on Dutch) simply are the best. Advice please...thank you!