If my EBF LO was a bottle champ...

How many ounces should he take at one session? He’s 12wks old (preemie so his adjusted age would be 7wks). I let him nurse on demand, but he’s pretty consistent every 2hrs for approximately 7-10 minutes. I’m asking bc I’m going back to work in 3 weeks and he’s going to have to take the bottle while I have an 8hr work day. By the time I commute it’s more like. 9.5hr day. About a month and half ago, he took 5oz from a bottle. Now we are lucky if he takes 3oz. I will admit I have not been consistent with the bottle the past couple of weeks due to him having RSV. Last question, should I try switching bottles? We started out with playtex drop ins and switched to Avent. Wondering if a switch would help.