He sounds like a fabulous little boy - and loves his boob. I agree with what others have said. It sounds like he is getting plenty of milk at the breast - and there doesn't sound like there is any need for formula top ups. Unfortunately, formula top ups generally mean breastfeeding finishes sooner than the mother would ideally want - and most mothers stop because they find it hard to believe they are making enough milk.
Baby sleep cycles are about 20-40 mins in length - babies will come into a lighter phase of sleep at this time, and will need to be held and cuddled back to sleep, but not always fed. It's not the case that babies only wake and cry when they are hungry - they can do this for a lot of reasons - lonliness, boredom, wet or dirty nappy. they have a great need to be with their mum or dad. Understanding how babies work can give you a whole different perspective on what they are trying to tell you.
Any breastmilk you give your baby is fabulous. Some mums must give a little formula and this can work fine too - the breastmilk helps baby digest the formula. Unfortunately, it can have a nast habit of "creeping in" more and nore