Sleeping 20 hours a day at 11 days old is actually quite normal, newborns can sleep up to 16 to 20 hours, and waking them every 2 to 3 hours for feeds is the right thing to do since they sometimes sleep through hunger at this age. For formula amount, a rough guide is that newborns generally take about 60 to 90 ml per feed at this stage, so if he is finishing 60 ml and still showing hunger cues like rooting or sucking on his fist, you can try bumping up to 70 to 75 ml and see how he goes, my friend's paediatrician at KKH actually told her to go by hunger cues rather than stick rigidly to a fixed amount, which made a lot of sense. The general rule of thumb going around is about 75 ml of formula per kilogram of body weight per day, so your baby's weight is a good anchor to work from when deciding how much to increase. That said, since he is on a mix of formula and breastmilk, the balance can vary day to day, so it is worth checking all of this with your PD or a lactation consultant to make sure the amounts are right for his specific weight and needs.