Hi Dan, Yeah, get a down bag, the same as what you have, only opposite zip.
While there are a few people out there that find mummy bags a bit confining for couples, the wife and I have been going out for 35 or so years using zipped together bags. If it is too warm, like 40F or more, we just lay one over us and sleep on the other. You can easily extend a bags warmth by 10-15F by zipping them up and sharing body warmth. We were often out in October with summer bags.
A sleeping system is one of those systems that must function on longish trips. You must have some sort of cover against rain and the elements. In spring and on warm summer nights, bug protection is needed. A good pad also lets you sleep fairly comfortably. The wife found foam pads inadequate. She instantly fell in love with the old NeoAir. In the ADK's, it is easy to find softer fabric soils or duff. Combined, a 3/4" pad and about 6" of duff kept her hips happy before inflatables. We were never comfortable in lean-to's and on platforms so we used to avoid them.