So, how do you feel about your risk perception now, OP, after reading the responses here?
I think I still feel comfortable. On one hand, I think many people did misunderstand both the quality of building, and how long we were leaving our baby.
For those who didn't misunderstand, many have put forward a kind of zero-risk approach to childcare, which simply is not feasible as people have pointed out - we all take risks with our children to some extent.
Knowing the layout of the house and garden, we feel comfortable that the risk of fire is extremely low, the risk of child abduction is very low. Yes, something could happen, but the door to the guesthouse is in sight, a monitor is on, etc.
For at least 22 hours a day (this week, on average, I'd actually put it at 23 hours), the baby is in the same room as its parents or grandparents. The baby is only on his own when sleeping, not when he is awake.
The risk of SIDS, I appreciate, but that seems more like an argument for not sleeping. Any baby could encounter problems either when we sleep next its parent, or if it were upstairs, and it would be easy to miss.