When its cold I use two pads, my inflatable thermarest and my Z-rest, sort of overlapping. Usually I then use my mummy bag like a quilt, draped over me. I am a pretty warm sleeper though. This has taken me down to about 20 degrees F. For 50 degrees or so I can generally use just one pad, with the bag tucked under me. It takes a non tosser and turner to sleep like this in cool weather.

I have used a fleece blanket in milder weather, it does insulate a bit but not as well. I have found that a sleeping bag no matter what its rating will compress to much on the bottom. My old -15 bag would be to cold on the bottom and sweaty hot above in cool above freezing temps. Still needed the pad. Never used an under quilt, or a reflector.

The trick to getting a tight mummy zipped in the hammock is to partially zip it before you sit down, about up to the navel for me, just so that the but area of the bag is stable when you put your weight on it. Sit on the pad, swing your legs up into the hammock with the hood sort of over your head to keep it from bunching in the small of your back. When you are adjusted right then you can zip up.
One thing I usually do is to put the pad in such a position that when my but twists into the hammock with most or all of my weight on it, it moves a bit in the direction that I am twisting, so that it is positioned right when I am in. this takes practice but it is possible. I am actually faster getting into my hammock than most people are settling into a tent.