Hammocks really are great! While I don't personally know of any pads that work well to add warmth to a hammock, I have made 3 different top quilts before which are very similar to an underquilt. Making your own is a great option and you shouldn't be afraid to try it! My top quilt was actually my first sewing project and it was a lot of fun. The most expensive part is usually the down insulation, but you can use down from good quality pillows if you decided to go this route. Here's a blog post that I did about making my third top quilt: Here
Let me know if you have any questions about making an underquilt if you decide to go this route!
I’ve used a simple nylon mesh hammock and a rainfly as my lightweight backpacking sleep/shelter solution for years. Initially I just lined the hammock with whatever clothing I wasn’t sleeping in, then put my sleeping bag on top of the clothing. This provided only a spotty, lumpy layer of cushioning insulation. A big improvement is to first place a narrow air mattress in the hammock (a blow-in mattress, not self-inflating). Besides an insulating air space, the mattress adds some support and stiffness to the hammock. Since it’s not on the ground the mattress isn’t subject to risk of abrasions or puncture so can be quite lightweight and inexpensive. Another detail I found important is to vary my sleeping bag’s weight, style and materials depending on the season; and to do the same for what clothing I sleep in. For example I found a hooded mummy bag with a full length zipper provides the most ability to adjust the bag’s position in the hammock and around my body; and is also the easiest for me to get into and out of when using the hammock. I’ve sometimes put a reflective “space blanket” between the hammock and air mattress as an additional layer but I’m not sure if it helps retain body warmth or not. In bug season I toss a rectangle of mosquito netting over the rainfly and clip the bottom edges to the hammock with plastic clothes pins. I usually carry a second mesh hammock and lightweight rainfly so that where possible I can have a dry place off the ground for my pack and gear. This also provides a separate spot from my sleeping area to hang wet rain gear etc. My hammock sleeping style has been comfortable even in very rainy, snowy winters in the Oregon Cascade mountains. It may leave you much too exposed for sleeping in sub-zero weather.
I use the Big Agnes Superlight Q-Core pad. Light weight and it has kept me comfortable down into the 30's... (never had an opportunity to try it below that since I bought it).
I started with a 40-degree underquilt. After being really cold on a three-day, two-night backpack in Virginia, I invested in a 20-degree underquilt. But I backpack at least three or four times a year and am hoping to raise that number. I don't see making my own quilts in my future, as Noah mentions. But if that's doable for you, it's an excellent option.
Does anyone have any experience with either making your own top quilt (down preferred) or do you have a top quilt you recommend. I’m usually a relatively colder sleeper than most. I’m really looking to shed some weight from my sleeping bag and would like to get the weight down to about 1-1.5 pounds.
Therm-a-rest makes some really nice quilts. I have a corus HD and its rated to 40 degrees so its keeps me warm on the chilly summer nights but comfortable on warmer ones too. It weighs 1lb 8oz so a little heavy but worth it!