At the end of the day you have to do whatever suits you and your family best, whether that be bfing or ffing. However, having done both I can hand on heart say that I have much preferred breastfeeding.
It's really really tough in the early weeks. Baby cluster feeds, feeds take ages, they're not satisfied and they want to go back on constantly and so on. Your nipples are sore and all you want is some time with a baby not on your breast. I understand completely because I've been there. But that's the thing, you really are in the early weeks.
My son is 3 months old now and breastfeeding is so so easy. He feeds for about 5 minutes and then he's done. I never have to faff around with bottles or sterilising, worry about where I'm going to be and how I'm going to warm a bottle up.
First time around I FF. I switched because I didn't understand what was normal for a BF baby and because I was struggling with a lot of emotional 'crap' in my life and couldn't cope with breastfeeding on top. I do not regret it. I never beat myself up over it. I did what was right for me at the time and my eldest is a happy, healthy boy.
Bottom line - do what is right for both of you and if that is formula that's absolutely fine.
But I just want to re-iterate something that someone on here said once (can't remember for sure who it was!). Never quit breastfeeding on a bad day. Because the next day might have been better. Take time to think about it logically and without too much emotion. Then switch when you're sure. It's a decision you most likely won't be able to change once you've done it, so make sure you're certain.
Completely agree with this entire post, well said. I much preferred breastfeeding as once you get past the initial newborn stage, it really is loads easier than bottle feeding. Its definitely HARD at first. cluster feeds are exhausting, sore breasts are irritating, wondering whether you are making enough is stressful. But then they get a little older, and it suddenly gets loads easier. They go longer between feeds, feeds are much quicker adn efficient, there's no clean up afterwards for bottles, etc (unless you are pumping while working, of course).
I breastfed DS1 for 4 months, and ended up switching to formula once back to work because my supply dipped so low that it just ended up causing too much stress. Nothing I tried increased my supply. I felt guilty at first, but then I realized he was just as happy as he ever was, and he was still a healthy little boy.
DS2 I breastfed for 6 months, and had another month worth of milk in freezer so ended up being 7 months of breast milk. I had to quit because my coworker moved out of state, and I just literally did not have the time to pump at work anymore. It wasn't that they didn't allow me to, it was that if I had actually taken the time to pump every day I would have had to work that much overtime everyday to get the work done. I felt incredibly guilty quitting with DS2, because it wasn't even a supply issue and we were doing so great with breastfeeding. But at the end of the day, I just didn't want to sacrifice time with my boys to work overtime so that I could pump at work. So although I felt guilty for a while, looking back on it now, I am happy with my decision. I wouldn't trade that time with my boys for the world.
In the end, you have to be confident with your decision. Take a good amount of time to think it through and make sure what you decide is really what you want to do. There is no wrong answer here, but you DO need to be okay with what you choose.
Also, just wanted to add that the weight gain she has made seems fine to me. She could have been a small baby full term anyways, you have no way of knowing. DS2 was only 6lb, 12 oz born at 36 weeks, lost 12 oz first week, then gained back birth weight 2 weeks later (he was jaundice though so weight gain slow due to that. But still, he was gaining). there is no right amount of weight gain, either, its just making sure they are gaining weight. Some gain slowly, some gain super fast. Don't worry too much about the numbers as long as she is gaining.