I only lasted 4 weeks breastfeeding my first too. It was sapping my will to live. Honestly.
This time I know what to expect, and hope to do it longer.
When I gave up breastfeeding I talked to my maternal health nurse, here's what she told me.
Infant formula is based on cows milk, but has other nutrients added, and certain things removed to mimic breastmilk as much as possible, as long as you mix it exactly as directed. It has more iron than breastmilk, but it is in a form which is herder to absorb, so that kind of evens out. It also has more sodium so it is important to offer plain boiled water to infants who are formula fed. The baby does stay full for longer which is why people who breastfeed during the day sometimes give a bottle of formula at night- just for the extra couple of hours sleep.
Out and about, you will have to either carry the correct amount of powder and hot water unmixed (and separated into separate portions, if you will be out for more than one feed-unless you want to bring the special scoop and everything), or mix it before hand if you can keep it refrigerated, then heat it up wherever you are going. You have to be fastidious washing and sterilizing absolutely everything that comes in contact with the milk
plain cows milk should never be given to infants lass than 12 month of age. It can be harmful, even if it's boiled.
Breastmilk is better as it is designed by nature. The milk in the first few days is full of immunities to illnesses, and to a slightly lesser extent, this continues later on as well. It is always with you, and always ready to use. However, it is not as easy as you think, and you will spend a lot of time worrying about how much the baby is getting, you will have to feed more often, you will lose sleep, even when you are not actually awake and feeding, you will dream that you are, or wake up in a blind panic with nightmares about falling asleep on your baby during a feed. You will lose your mind a little bit, for a little while. You will have to get your boobs out in public and, worse, in front of your in-laws!!
Expressing milk for bottle feeding has almost all of the disadvantages of both breastfeeding and bottle feeding if you're going to do it all the time. ( I did for a week or so, so that I could continue providing breastmilk, without feeding from my poor suffering nipples (they were in a pretty bad state, and bleeding during feeds)
you have all the bottle etc. Cleaning combined with all the bits and pieces of your breastpump. You will have to express milk as often as you would have been breastfeeding anyway- and you'll either be doing this"on demand" while the baby is crying for a feed (and it usually takes two hands to express, so you can't hold the baby at the same time) or you will be spending a crazy amount of time attached to that pump trying to keep a feed ahead of the baby while it is sleeping, instead of resting, which you need to do to keep your supply up. If you do manage to keep a fed in advance at all times, you will be faced with the same storage and warming issues as you would with bottle feeding. Breastmilk can only bee kept in the fridge for 12 hours, but can be frozen for 3 months. Overheating it will result in most of the nutritional benefits you are trying to keep being lost.
It is handy to be able to express milk on an occasional basis, to leave your baby with a sitter, or have your partner do a night feed, but you can't live like this and stay sane. I tried.
I eventually did give up at about 5 weeks, and besides 1 minor cold at 14 months my daughter (now 2and a half) has never, ever, ever been ill. Not so much as an upset stomach.
My nurse told me at the time, that the most important thing for a baby, was having a happy mother, so if breastfeeding is making you crazy, it's better to switch. Torturing yourself will make nobody happy.