My girls were also prem (33 + 6) and I did mixed BF and EBM bottle top ups until they were 10 wks. They fatigued after about 10 mins at the breast till that time.
I kept expressing as we did an evening bottle too - cluster feeding 2 wee bubba's was more than I could handle. And I bottle fed when out cos tandem feeding was more a in the privacy of my own home activity
(suffice to say I didn't get out much in those early months)
Edited by Danda08