For the way I sleep, a bag is not overkill. I toss and turn a lot. With the typical bag and pad, I wind up sliding off the pad and wake up freezing my tail off on the ground. I suspect I would have similar problems with a quilt and pad.

I've gone with the Big Agnes system of having the pad captured in a sleeve on the bag. It works extremely well for me, with the bag zipped up I never slide off the pad. I really like the Horse Thief, mostly because it doesn't have a hood (I wear a cap at night). I have been comfortable in it to the low thirties, but wouldn't want to go much colder- although I have not tried sleeping in pile insulated clothing (Patagonia Micro Puff). I do normally sleep in my clothes.

Be aware that if you camp at altitude, it can be significantly colder than lower elevations. Especially in spring and fall. A decent 40 degree bag might fill your needs.