S.,
I'll tell you straight off, I'm a breastfeeder. I bf my son till he refused to take any more, and will breastfeed the one I have on the way. I am too lazy to wash bottles, mix formula, sterilize stuff, etc. It's a pain in the neck, and it's too expensive.
That said, YOU make the decision that is best for you and your family. DO NOT let anyone on here, or in your family, or in your circle of girlfriends pressure or guilt you into anything either way. Formula is not poisonous. A bottle given with love, with a warm and open heart, beats a breast offered grudgingly, or with resentment. Your little girl will know if you feel badly about nursing, and it will cause feeding issues and a difficulty in bonding.
Now, the first few days of nursing is often difficult. They made me supplement in the hospital with my son, too, and it wasn't until I got home and took the bottle away that he really did well nursing. It's easier to drink from a bottle, and he was lazy. Within 24 hours of exclusive breastfeeding he was a champ. Not all babies work that way, though. Some need to be taught how to latch on properly. That is the number one cause of nipple soreness. An improper latch can get you every time. There are extensive resources on the internet for pictures and descriptions of how to latch the baby. If that doesn't help, call your pediatrician's office or La Leche League, and arrange for a lactation consultant. She will come to your home, and watch you nurse. (Don't be embarassed, she's far from the last person who will see you do it!) She'll show you what might be going wrong, and help you re-position her so she can eat properly, show you howto teach her to open her mouth wide enough, and anything else that may help you out.
A breast pump would be a wonderful item for you right now. It will help to relieve engorgement, and your boyfriend can give her a supplemental bottle of your milk, instead of the formula. Pumping regularly in addition to nursing will help you build your milk supply, so you'll know she's getting enough to eat. I bought a one-side electric model at Wal-Mart for like $35 when my son was born, and it was great for me.
If you decide that you would prefer to bottle feed instead, it won't be difficult to wean her. You may have to try a few different brands of bottles until you find what she's comfortable with. All babies are different and their nipple preference on a bottle varies with the size and shape of their mouth, how often they breastfeed, and how like mommy the bottle nipple is. That's just trial and error. The bigger deal will be drying up your breasts, and that's incredibly painful to do all at once. Don't pump to relieve the pressure, because that just stimulates your body to make more milk. It's gonna hurt, a lot. Cold compresses help, some women even put cold cabbage leaves inside their bra. You're going to leak like mad if you do this, so good nursing pads will be a must.
Good luck S., and make the decision that feels best for you and your family. Throw the parenting books away, and raise your daughter with love and joy!