Last year I made a winter topquilt and my feet were usually cold, unless I stuffed the footbox with my down sweater.
The problem was the draw string closure at the foot end. So I had to make a sewn in bottom and increase the leg room width because I was squishing the loft around my calves. Another problem was my foot pad wouldn't stay in place so I had to deal with that too.
My first attempt at modifying the foot end I made a circle with a 3.5" baffle in the center, sewn through around the circumference, and attached to the foot end. But I noticed a problem. When I got in to test it out, my toes would be pointing right toward the seam between the two. No insulation in the seam and cold tootsies.
To rectify the leaky seam I made a rectangular plug, 4" baffle in the center and 4" height around the perimeter 5" loft. Also,I expanded the foot end from knee to foot and made velcro attachments for the pad.
No more cold feet and heres some pics.