>>845131There are hammocks that you can sleep on your stomach, such as bridge hammocks, although stomach sleeping is linked to many health problems, and you should avoid it.
Moving around in your sleep is not an issue, you can roll side to side all you want. Even in a typical gathered end you can pay mostly on your stomach without issue. Many people find sleeping in a hammock they have no desire to roll around since unlike a pad in a tent, you're incredibly comfortable and supported. You just drift off to sleep without any of the typical tossing and turning.
They aren't for everyone. There is a learning curve that many people just don't want to bother with. There is a "fiddle factor" to get the most out of a hammock set up.
Agree with the no tree issue, however I live on the east coast of the USA, so there is not ever a spot without 2 trees in sight.
They are fine when it's cold. I've slept at 0 degrees before. As long as you have proper gear, you can sleep at minus 40 degree F temps (Google shugemery in youtube, who has a video doing it).