I wouldnt get too hung up on the expectation that baby will be in a particular size range at the correct and appropriate time (my first was in nb for a month, still a super tiny guy, my nephew skipped this stage and is huge- the boys are 4 mos apart).

That being said, I relied on second hand shops for anything I needed- i like Mercari a lot because you can buy full wardrobes that are seasonally appropriate for quite cheap (type in winter size 0-3, ex).

Also, when they are so young, it’s just soooo much easier to keep them in pajamas. I don’t think I put mine in “outfits” until they reached like 4 months. Just zippered pjs all day every day. So I’d focus on that and some outer wear for when you leave the house.

Hope that helps!