BMW replaced quite a number of loose stitching items on my 318i out of warranty but that was almost 7 years ago. Their policy might have changed. Show us some pictures on your seat.
The build quality of the 1M is like other 1ers. I do find the 5er are the 3er are built to a higher quality standard. Whilst the X3 was a bit worse and x5 on par.
Macan Turbo - White
1///M - Valencia Orange
X3 30d - Alpine White