Confused, you need to do what is right for you, but the things you mention as 'proof' you aren't enough for your daughter, aren't in fact, anything of the sort and it sounds like your confidence has been undermined and destroyed, perhaps not really help by your obviously well meaning DH either.
presumably you chose to breastfeed because you believed it was best for your baby and those reasons still apply.
It's normal for breastfed babies, even full ones, to take a bottle keenly. A bottle is much less work for them than breastfeeding is and having a bottle of formula, which is much harder to digest than breastmilk, is a bit like having a huge Christmas dinner. The baby feels very full and very sleepy afterwards. This is one of the reasons giving any formula can be bad for breastmilk supply, it spaces feeds out. On the other hand, breastmilk is easy to digest and babies don't only want to be at the breast to feed.
Plus, as has been said above, there is often a growth spurt at around 6 weeks, which will mean your baby will feed much more often, maybe almost constantly and she will do that partly in order to increase your supply, so giving extra formula at that time can be counter productive as your supply won't increase.
As has also been said, it has been very hot, which can also mean more frequent feeds are taken, to quench thirst as well as hunger. Imagine how much more us adults want to drink when it's hot.
It's also possible there is a problem that can be fixed, so if you want to continue breastfeeding then it's worth getting some good help and support, maybe through your local breastfeeding clinic or the hospital infant feeding advisor if you can? Or one of the breastfeeding organisations such as La Leche or Breastfeeding Network.