My girlfriend and I have some of the same issues. Our shelter takes care of the mosquitos, but she needs much more insulation at night than I do. We share a single double-wide quilt, but use two separate sleeping pads. Hers is a thick, down-filled inflatable pad over a thin CCF, and mine is a Synmat UL7. I attached some kamsnaps to the quilt on her side so she can snap both of our down jackets, her down vest, and her down pants to the top of the quilt on her side. This doubles the volume of down over her. Also, she often wears a balaclava to bed, while I don't.
Every couple has different needs, but for us, sharing as much as possible (shelter, quilt) saves weight and keeps us warmer. The provisions I mentioned above make it possible for us each to be comfortable.