We were worried about this with our first. So we placed her in a low/soft walled inner cot box between us in bed. It gave a boundary you could easily feel when sleeping and seemed to give the best of both worlds.
The other strict rule we had was if someone had a few drinks, the baby slept in the cot or you slept on the couch. A nurse told us that largely these smothering baby tragedies occur when someone has had a few drinks.
When we coslept with our first kid, I almost rolled over onto my daughter once - she squaked in a way that I would never be able to ignore - unless I had been medicated.
The other strict rule we had was if someone had a few drinks, the baby slept in the cot or you slept on the couch. A nurse told us that largely these smothering baby tragedies occur when someone has had a few drinks.