I went to Sage a few times in the last couple of months, I did not pay much attention to the baby girl section but in the baby boy section they had adorable cozy velour and non-velour stretchies and outfits in all different styles. So far what I'm using from them is great.
Tottini would also have stuff.
In the past I've found velour stretchies (more casual) on Amazon too.
The stores usually have night hours on at least some days during Yom Tov season, if you cannot make it there during the day.