Try to avoid hot tub hot where there is steam. I have to keep mine a little warm or I freeze lol. As to sleeping on your stomach, I would say the first trimester is ok to do that but I would definitely try side sleeping in the second trimester. I put a pillow between my legs and lay against a body pillow at my back to keep me in that position, otherwise I tend to roll either on my stomach or my back in the middle of the night. They say that laying on your back in later pregnancy isn't good either because it puts pressure on your nerves and spine. I tend to find that it makes me a bit nauseous when I sleep on my back for long periods of time in pregnancy.