I hope someone more familiar with BA sleeping bags will pitch in. Most of their bags are based on no underside--just the sleeping pad in a pocket. Since I do lots of tossing and turning at night, and learned from childhood to take the sleeping bag with me when I turn over, I'd invariably end up with the pad on top! Your mileage, obviously, may vary!

My own experience with a 2-person sleeping bag is that they are quite drafty. Inevitably one of the partners will move so as to let cold air in. If it's a cold night, I'm much warmer in my own bag with both hood and the draft collar (around shoulders) drawn up really tight. IMHO, a better solution is for each of you to have your own sleeping bag but have compatible zippers (left zip for one and right zip for the other) so you can either zip them together or sleep separately, whichever you prefer. That also lets you each go alone without having to buy another bag!