Technically you don't NEED an underquilt, but some form of insulation. Eno Hotspot is a commercially available way of extending your pad that is based on the Speer Pad extender.
You can get by ok with pads.
See also the Garlington Insulator.
my hammock gear weights total: 2430g (~86oz)
Winter: total 2521 (~89oz)
(see my profile for detailed weights)
gram counter, not gram weenie!