Jacket for 3-6/6-9 months

Linda • 23, married, 3rd pregnancy, but first baby that stuck 😊🌈🎀
Does a 3-9 month old really need a jacket? Or would you think it would be ok just to have sweaters and warm outfits? Baby probably won't be outside much (and if she will be, then obviously I'll get her a jacket/snowsuit). 
I heard it wasn't safe to put a baby in a thick jacket in a car seat.