Boleh je mix, tapi kena gradual transition kalau nak tukar formula, jangan sudden switch sebab baby's tummy boleh jadi upset. Few of my mum friends ada yang guna 2 brands gak, usually sebab ada stock issue or baby tak tolerate one brand, tapi ideally consult dengan pediatrician dulu pasal setiap formula ada composition yang slightly different, better safe than sorry kan, especially at 1 month old. Kalau baby okay lang with both and no digestive issues (i.e., normal poop consistency, no excessive gas or crying), then okay je, but if ada rashes, constipation, atau baby jadi fussy, stop and check with doc. Good luck!