a 3/8" thick pad will keep you pretty warm. The biggest issue for an adult is that it won't cover your hips and shoulders.
Some "wings" made from another pad, or a cheap silver windshield reflector turned sideways will help quite a bit.
How cold are you planning to go?
Not sure what temps that you will be sleeping in, but I would guess that below 40 degrees f, you will be a little chilly. I used a car windshield reflector for bottom insulation and was a bit chilly in temps around 38 degrees.
We'll probably be going in a fortnight so it could be as low as -1 or -2, I thought about getting some survival bivvys for lining the hammocks they look like giant triangles of silver foil and are only a couple of quid, I use a british army issue arctic sleeping bag with army issue bivvy but the boys will have 4 season bags
Sorry I use oC