If you are committed to breastfeeding, you can do it. Your baby won't get hooked on formula, but she will get hooked on bottles, since they are much easier to drink from than your nipple. Be adamant with the staff and everyone around d you that you only want to breastfeed, and ask for help from the hospital lactation consultants if (when!) you are struggling or doubting yourself or your body. You can do this!! Good luck :-)
I can't lie on my back for very long, it starts to hurt. That's when I know it's time to move. I wouldn't worry too much about it. Your body will tell you if it is uncomfortable.
Breastfeeding is different for everyone. The hospital will not make you feed your baby formula and there should be lactation consultants on hand to answer any of your questions and show you what to do.
I lye on my back alot after awhile i start losing my breath and i turn sideways or sit up, i don't think the little amount of time you're spending on your back is a big deal, the breastfeeding situation i have no experience with that