I bought a simplicity (3584) pattern a couple of weeks ago that has 2 piece pjs, for summer & winter & a dressing gown, in unisex size half - size 4

It has both a T-shirt style top & a button up top. Buttons wouldnt be an issue as long as they are sewn on properly, Ive had DD in button up pjs since she was around 8 months, or you could replace them with snaps which come in a set (you'd need a hammer to apply them) or the strip snaps as suggested by Kate