as far as the falling alseep at the breast, just rouse her a little when she starts drooping. most breastfed babies will try to suck back in if you start removing the breast just when they are falling to sleep, or you can pull her closer to you and see if she starts sucking more. just rouse her in some way, talk to her, tickle under her jaw, stuff like that.
CONGRATS ON BREASTFEEDING! :D its the awesomest thing ever.
one thing that ive heard about getting breastfed babies on the bottle is that mom might not be able to get baby to use the bottle. when it comes to that, babies arent stupid, they can smell you and they know the real thing is there somewhere, they prefer that thank you :P. so you might have to leave the room completely and have someone else take over bottle duty to get her to take the bottle.
also, when it comes to breastfeeding you should never worry that shes not getting enough. your breast is always enough for your baby. with VERY rare exceptions, there is never a reason to supplement with formula, though doctors (who work for clinics and hospitols who are paid by formula companies) are quick to suggest this as a remedy to nursing moms who are concerned about amounts and that sort of thing. they dont have the time to sit there and educate you, so instead they take the easy way out and just hand you the formula line. dont fall for it unless you are SURE yourself that shes not getting enough.
ALSO, for babies whos moms go back to work or school, there is a common theme of nursing or bottle 'strikes' - where baby will just refuse to eat. this is ok. your baby will not starve herself. make sure the caregiver just keeps trying to get her something to eat during the time you are gone, and be fully prepared to spend extended time reconnecting with her when you get home. she might actually learn to nurse longer and eat more at a time when she does this 'strike' than normal. always make sure that before and after you leave you spend close personal time with her. i highly recommend getting a sling of some kind - the moby wrap is VERY comfortable. you can go about your morning routine for the most part with her strapped to your chest, and you can transfer her right to the caregiver in the sling so that baby has another person to snuggle up against that way after you leave. also, when you get home and want to do something, you can pop her in there and go about your business all while reconnecting with her. :D
as far as popping a boob in every time she is fussy, congrats! this is healthy and awesome for your relationship and her needs :D its responsive parenting, and thats what you WANT to be doing. however, its perfectly normal to want to stop doing that at some point, and you can introduce a pacifier at any time, though again, she might not be intersted. babies lose them so easily and its frustrating for them, and for you to have to get up every so often and give it back you know? its up to you. some babies do just fine without a pacifer, but im telling you that sucking is a NEED for babies, and an unfulfilled need turns into an undesireable habit later. i know a baby who didnt get a pacifier, and he ended up grinding his teeth, which hurts mine! :O
anyway,
good luck. this is a hard time for you, and the more sensitive and responsive to her needs you are, the easier the transition is. find a local or nearby la leche league, they are FANTASTIC and i didnt start going until my son was 16 months old or something, but i regretted not going sooner. they are so encouraging and helpful - you might need and LOVE their advice and support and encouragement. do your best to get to the next meeting you can find. i know they have a list on their website
http://www.llli.org/
there might not be one in your specific town, i drive an hour to get to mine.. but there is usually one nearby
so check nearby towns as well as your town
good luck! and have patience and confidence. ! :D