We booked for bassinet seat from SQ a couple of times and no issue. Even if baby is in bassinet seat, during air turbulence, take flight and landing, baby needs to be carried out and buckled strap to you. Some parents babywear their baby on flight. My children only slept in the bassinet for midnight flight. No issue but it's also dependent on each individual babies.
You can bring along baby's pillow, blanklet or soft toy to make baby comfortable.