I tried a silk liner once. Got thoroughly tangled up, every time. In addition, although the package said it would add 9*F to the bag, I could detect absolutely no difference with it or without it.

Since I sleep cold, I'd rather have a warmer bag. Some try wearing more insulating clothing (down jacket and pants) inside a warmer bag to stretch the rating. Works for some, not others.

If you're going to be in northern Minnesota, I'd suggest a 20* Western Mountaineering bag--Ultralite or Megalite, depending on girth needed. Be sure to measure shoulder girth over your arms while wearing all your insulating clothing. That will take you down to at least 15*F or a bit lower, if your sleeping pad is warm enough. If it's a hot night in summer, just leave the bag unzipped and lie on top or use it as a quilt.