I know there is only bedding for four, but are 5 people allowed to sleep in a one bedroom villa? If so, What type of bedding have you brought for this situation?
So I went back and did a double check it seems that BCV does allow a 5th in the 1BR but I haven't done it just read it on other threads over the years when I did a search.
Sleeping bag for a kid would work best for the space and easy to get out of the way. A blow up mattress is an option but I would worry it would make it tough for people to move around and you got to store it during the day.
We went on a cruise once in a 2br suite on NCL and just brought sleep bags for the kids and they loved it.