You can't go wrong with a Warbonnet Blackbird for comfort and bug protection. With a 26% tariff and international shipping I think it's still worth the price.
At 40F/4.44C any pad or 3 season underquilt should work well. I like down but where I'm from, when it drops below freezing the air is usually dry, but for wet conditions it's good that you're considering synthetic insulation.
If cost is a big issue I'd put my money into a hammock and tarp first and make due with the pad and sleeping bag that I already own, while I saved up for quilts.
PS Hammocks aren't always the lightest option when you're camping in the extreme cold, but they sure are comfier.