My wife wants to have another child but i'm not sure if i really want another child?

My wife and i have been married for 21 years we have three children together two girls and a teenage boy ages 16, 12 and 9 we have been fortunate enough to have such wonderful children we both work i am a paramedic and she is a kindergarten teacher. We have great jobs, so my wife have been talking about having another child she keep saying how great it will be to have another baby. She keeps bringing it up she even ask my kids if they want another sibling and they said yes!!!!!!! But i'm not sure if i really want another kid and she works with kids and she loves kids. I asked my father for advice he said to follow whats in my heart. I have 4 brothers and 2 sisters he told me this " Son me and your mother love our children very much we wanted 7 children and that's what we got and i thank god every day for giving me that gift and always follow what you know is the right thing to do in their heart". So what should i do i'm on the fence about having another child and i don't want to cause any problems in my marriage.