I think marks and Spencer still do them but they have a shirt with a button on the inside to stop them popping open! They have a seam so you dont see it. But could always sew one on x

Lol I must be exactly the same with my shirts then lol, but hey ho if it's a comfy shirt what the hell it's worth fixing :) I know from experience button holes get looser the more they get fastened up so just try stitching it up a bit to make button fit in more snug :) don't be embarrassed joys of motherhood an having larger boobs :) lol xx

Aww bless lol, I've had this before I safety pinned it , but you could try sewing the hole a little smaller so button can't pop out easily , other than that I'm stuck what to say :) lol x