Alright here's what I currently have. Under Armour Infrared Base 2.0 under Under Armour Ayton Storm fleece lined bibs & jacket. I stay warm and comfy down to around 40°. What is my best option for when temps drop below 30° and into the teens and even into single digits? Should I use my Base 2.0 as a bottom and get some Merino wool mid layer? I've considered the UA Base 5.0 as well. I'd like to keep the bulk to a minimum but warmth is my #1 priority here.