Do you know why the kid is waking up at night?
My youngest started sleeping through the night perfectly at 3 months old (yes we're lucky).
However, at around 9-12 months she started waking up at night again... almost every night.
It turned out that she was well fed with bottles but as soon as we started giving real food, she ate less and always woke up at night because of hunger.
We started insisting a bit more that she ate full portions and since then she's not waking up at night anymore.
We never co-slept with our kids though, because it's so hard to get rid of it when they are used to it.