I am curious about a couple of things. Why would you want to wear a jacket inside the bag? What temperatures are you trying to sleep in?

I never use a bag in three season conditions because I found them to be too constricting. For temperatures down to the mid 20s (f) I use a quilt and don't require additional insulation. Some quilt users will get to 0 before switching to bags (there are 0 degree quilts).

Too many layers can be self defeating. If you bundle up so much that it restricts your own blood flow, you'll have trouble staying warm.