Sparkly, that's a very sad decision to make!
Can't you just refrain from kissing when you have an active outbreak?
Remember that the majority of the population carry the cold sore virus so your child could just as well become infected by little friends at the nursery, love kisses etc...
Even if your child gets the virus (which will probably happen anyway) it doesn't mean that they will suffer like you do.
My mum has always suffered from cold sores. She refrains from kissing and sharing bottles or cups or anything like that when she has an active outbreak. My dad, my older sister and I don't suffer from cold sores at all, my little sister has had them very occasionally. In all likelihood most of us will carry the virus but it doesn't exactly infringe on our lives (just like you carry viruses and bacteria for all kinds of nasty illnesses around without falling sick).
Never being kissed by our mother, however, would surely have a much bigger influence on our lives! Can you imagine? I have to admit that I would feel very sorry for your child if you carried through with this and rather upset that you listened to your silly sister who doesn't know what she is talking about.
Do speak to your doctor or midwife about your fears and see what the qualified people say Xxx