It sounds like you switched to combi feeding before your milk had even really come in. Breastfeeding is all about supply and demand. Your baby sucking at your nipples tells your body the demand is there, and then your body makes the hormones to create the supply. That's why breastfed babies cluster feed in the early weeks.
You should let your baby feed directly from the breast as often as possible. At least every 3 hours in the first month or so, more often if they want to. Some women pump to increase their supply but I tend to think that if your baby is feeding enough from the breast that will be better to build your supply.
As for what to buy, I would focus on things which will be useful to you if you find breastfeeding painful in the early weeks (which is very common) and feel like giving up. Most women rave about the Lansinoh nipple cream. I personally didn't get on with it because I found it gummed up my nipples and made it harder for the milk to come out which meant my baby had to suck harder and it hurt more. Personally I found it was much better to just squeeze some milk onto my nipple and use it to moisturise after each feed. But you could try nipple cream and see if you like it, if you don't it makes a decent lip balm.
I would also get some nipple shields, but only use them if you're finding the breastfeeding very painful. I found them very helpful for a couple of weeks in the early days when every feed felt like a razor blade to the nipples. I would put one on and get the feed started, and then when the milk was flowing nicely I would quickly unlatch my baby and remove the nipple shield. It was still a bit painful but much less than at the beginning of the feed. I really think this saved my breastfeeding journey with my first baby.
I would also recommend getting a Haakaa or similar. You can wear it on the other breast during a feed to catch any leaking milk, and it's also great for any clogged ducts. You can fill it with very warm water and a spoonful of Epsom salts and put it on with your nipple in the warm water and it will gently draw the clog out of your nipple. My Haakaa saved the day a couple of times.
These were the things that helped me exclusively breastfeed my first baby for over 15 months.
My second baby got the hang of breastfeeding right away, I didn't need any of this stuff at all, and we are still going at 18 months.