Remeber, too, that there are (apparently) lots of positive points for an only child. They are more likely to be:

more confident
organised
emotionally supported
high achievers
self sufficient
more mature for their age

Many siblings aren't close friends so I wouldn't feel any pressure on having a child for your firstborn; you can make sure that you are sociable to aid them to mix/share/socialise.

Having said that, my youngest (who, obviously, has always had to share) is uselss at it.

Do YOU and partner REALLY want another child? Or are you happy being a family of three?

There is no wrong answer x