how tall are you, can't recall if you wrote that already. I'm about 5'10" and a 76in long quilt works well, one with a toe box construction, so keeps my feet enclosed. You've said how a longer one works for you better, so you certainly have that as a reference.

With quilts, the system of a couple of small straps that go under your camp mat to hold the quilt in place actually does work well I've found. It allows you to toss and turn , keeping the quilt over you properly.
Like I mentioned at some point, if you are really planning to sleep out at temps getting any where near freezing, you'll appreciate a warmer campmat with a higher R rating, or some simple foam mat to go under your campmat, but they are super bulky.