For around $180, delivered, you could get a Potomac (synthetic) underquilt. Check with BlackBishop351, who makes them. You might want a long, so not sure if that'll be extra $$. You'd still need a top quilt although you could use a regular sleeping bag unzipped as a quilt.
I have used this underquilt with my HH Explorer Deluxe -- it works great down to around 30F for me, and I'm a cold sleeper too.
"Civilization is the limitless multiplication of unnecessary necessities." - Mark Twain
“I go to nature to be soothed and healed, and to have my senses put in order.” - John Burroughs