There are hundreds that swear by hammocks as the ultimate in comfort. My hammocking has only gone as far as the backyard, but it's something you may want to look into. You could also look into one of those super-cush down air mattresses that are about a foot thick, used by backcountry stuntmen. For me, I've never had a problem with a basic thin pad for mostly stomach sleeping, so that's what I use. It's usually other details that get in the way.
One, not being tired enough to go to bed. If I try to go to sleep earlier than I really biologically feel like it, I end up frustrated and restless. I like to keep occupied with some reading, writing, or listening until my eyelids go half-mast. Long days of walking also help wear me out, but that's more of a style element.
Two, temperature and moisture. It takes some practice and luck to forecast my clothing needs for an entire night of sleep, but having breathable, easily adjusted sleeping gear can make a big difference. I'd choose a sleeping bag you can get body parts in and out of easily, and that will keep you at the temperature you like to sleep at. Quilts fit well here, or use a sleeping bag that ventilates well when needed. As for clothing, it needs to not get clammy and be easy to take off or adjust without waking up too much. Hoods, hats, gloves, and scarves are easy to adjust. Pants, not so much. You can also bring clothing inside the bag without wearing it, just to add a thin layer.
Three, aches and pains. A good session of stretching at the end of the day works wonders for me. There's no reason to not do it. It will keep you flexible, keep the soreness at bay, and you won't tighten up as much overnight. You'll be able to adjust to a variety of different positions more easily. If absolutely needed, add your mild painkiller of choice.
Four, noise. Earplugs can be miracle-workers.
Five, food and water. Typical signs like racing heartbeat, headache, thirst, wooziness, restlessness are a tip-off. There's an element of timing here. I like to drink all I can when I've stopped, get rid of all I can before I go to bed. I notice that my heartrate will remain at a slightly elevated level if I haven't had sufficient water, salts, carbs, etc. to replace and replenish at the end of the day.
Hope that helps a bit.