Be prepared to sit on the couch/bed/chair, etc. and feed your baby and do NOTHING else for the first few hours/days/weeks. Eat as much as you can (porridge is very good for supply!), drink water all day, sleep when you can (look into safely co-sleeping if you're happy with this), take as many offers of help as possible--whether it be someone watching the baby while you shower, someone making lunch for you, someone doing laundry or housecleaning for you, and when in doubt come here and ask someone or anyone because I was in doubt A LOT those early weeks. Every time he cluster fed and wouldn't sleep, I thought my milk was drying up. Turning to knowledgeable people in those weeks made me carry on! And read this...
https://theleakyboob.com/2011/08/baby-explains-normal-newborn-behavior/
Also, not much point in being fitted for a nursing bra until after baby is born in my opinion. Buy good nursing pads, lansinoh cream, and a good nursing pillow. Attend a breastfeeding group if you want as well. They can help check your latch if you're unsure. And make sure in the hospital that you tell them you want to breastfeed and want all the help you can get and they are to not give your baby formula!