When I gave birth to our firstborn, my husband's cousin gifted us with a pack of Gerber Onesies that had 8 pieces in it. Before that, I did not even know that Gerber had onesies.
Anyway, what she gave us were onesies for 6-9 months, but since my baby was quite long, she started using the Onesies at 4 months old.
I am very happy with the Onesies. My baby is very active and letting her wear a top and a pair of shorts looks like she has gone through a wrestlig match. But not with Onesies. Onesies stay in place. And since it is made of 100% cotton, it is easily washable and dries up quite fast. It does not need ironing either. It is wash and wear, though we really iron for the baby's safety. It is also very cool and in a temperate country like ours, it is very important to provide comfortable clothing for the baby. Otherwise, they will really fuss.
My baby is older and much longer now. But I still let her wear the Onesies, this time as a shirt or undershirt.
I am not sure how much this one pack costs, but since my baby has used the entire set for the last 6 months already, it is really worth investing in such a product.