DS growing out of BG diapers?

tegss

I think that DS is growing out of his BGs. He is 2 1/2 and I am trying start the potty training process, but he really doesn't seem to interested quite yet. Baby #2 is coming in Jan so I was going to buy a few more diapers anyway, but I'm trying to decide if I should buy for DS (bigger diapers? training diapers?) or buy for LO#2 and hope that DS will be potty trained in the next few months.

Any advice?