Just so you know, the sleeping bag ratings (at least the EU's EN13537 ratings, the only "official" ratings around) assume that you are wearing a base layer and a hat inside the bag and are using a sleeping pad with R value of 4. Wearing less may mean the bag isn't as warm as its rating. For me, a cold sleeper, a bag is never as warm as its rating anyway. Individual "thermostats" can differ a lot.

I personally prefer wearing my base layer in the bag to keep it clean and me warm.

Your mileage, of course, may and probably will vary.