Well as a general rule I sleep significantly better with a cooler room which would probably lead to more dreaming. I also have noticed that when I sleep with a high fever, my dreams tend to be this crazy kind of nightmare where instead of anything scary happening, I am pushing myself to my mental limits trying to solve some kind of complicated problem which might as well be unsolveable (this can be anything from math/science situation to a physical task). When I wake up I often continue frantically trying to solve whatever task I had that night for like 5 minutes before I fully realize it was just a dream. My whole point in this is that temperature (internal and external) can definitely have an effect on dreams, although in reality I think the best enviornment for good dreaming would be whatever you find to be the most comfortable.