My mom is a 34″ bust, and the 33.5″ was so snug the jacket fronts wouldn’t have overlapped much at all. The 35″ will, hopefully, give her an extra inch or two of overlap.
My bust measures about 35″ around (with clothes on; bra is 34 band) and the 35″ jacket felt too snug to me; the fronts don’t overlap much and the sleeves are too tight (my arms are very average-sized). So when I make one for myself, I’ll make the 37″. This is a jacket, after all, and I’ll wear a shirt underneath it.
I hope this is helpful!