Babies and moms are all different. As another person said, this is not a contest. You do what you can do as a mom/dad and that is fine. As I once read "let's reserve judgement for those that beat their children." I'm sure that statement was partly in jest, but lets be real, in life, in parenting, in finances, in everything, people are somehow programmed to view themselves comparatively/competitively. It's hard not to, but just don't, you guys have a whole lifetime of parenting to figure out, and what is best for your family might not be what is idealized as the way to do things.
Until I met a group of like minded (and possibly very lucky?) moms, all of my friends that had children were not able to exclusively breastfeed. My group of like minded mom friends? All 7 of us nursed exclusively. The common denominator, with an exception of a few kids in the group, is that we were all birth center (not hospital) deliveries. Meaning we educated ourselves enough to not just choose the default with it came to childbirth, and we all took the initiative to educate ourselves about breastfeeding. I'm not saying it was easy peasy for us all, but I'm just saying we knew what challenges we might face, and how to deal with them.
I understand this is anecdotal, but the disparity leads me to believe that education is key. Unless she is weighing the baby before/after the feeding, it is hard to know how much baby is getting, if she is worried about it. Nursing is work for a baby, so when you hand them a bottle of formula where it just comes out with a little squeezy-squeeze, of course baby will devour it like you've never seen them eat before. I was told this in LLL meetings that I went to months before welcoming our first.
I'm not trying to make anyone feel bad here, I just don't want for people to think, "breastfeeding exclusively works for no one these days!!!" That's not true. It's also true that not every mom can breastfeed, and that those that can often have difficulties. When I was pregnant and the formula samples started pouring in, I got rid of them ASAP, giving them to families that were already using them. Because I was also told in LLL that many a fine nursing relationship has been halted in it's tracks by a well meaning dad seeing a frustrated mom, and offering to just use that sample so she can get some sleep. When failing to try to breastfeed for even a moment is an option, it can be a slippery slope the way milk supply (and demand) works.
My first was also hungry all the time. And I don't even know to this day if she was really hungry, I just know she was crying and I fed her. Because when all you have is a hammer, everything looks like a nail. OP never did say why he and mom believe baby isn't getting enough/she isn't producing enough. If you haven't seen a lactation consultant (a good one!!!) yet, I highly encourage you do this before jumping on the formula wagon if breastfeeding exclusively is important to you. If it's not, whatevs, it's your kid and you are doing what you can for him/her, and that's awesome IMO.
Sleep. I think my kids were normal in this respect, and normal is pretty darn bad when you are used to sleeping uninterrupted all night long and suddenly you have to get up every hour. As a newborn it seemed easy, then we started using that damn pacifier after the potential for nipple confusion was over. Fast forward to 9 months, I'd read a dozen books on baby sleep and my 9 month old woke up 13 times in a night I didn't think was so bad so I'd pop that sucker back in. (I never kept track until a book suggested a detailed sleep log. After that night I put the pacifiers away and we quit cold turkey. It got better, but not until after additional rough nights.)
But it's not easy. People don't talk about how hard it is, and I swear a lot of moms just plain old forget how hard it was when their kids have changed or grown. And it doesn't get easier, the challenges just change. btw, before you think I think I'm some kind of champion nursing/tandem nursing mom, I leave you with this. My kids, now 6 & 4, are in the costco shopping cart that is next to our car. I grab some groceries and start arranging them in the car, and then hear screaming. The are halfway across the parking lot aisle and gaining speed. I run after them and catch the cart, everyone is fine, but I sure feel like mom of the year, right?!