All 3 of ours sleep with us...err...I mean...
we are allowed to sleep in the bed with our 3.

And it's not them that run the risk of falling out of bed, it's me.

Basically they sleep between my DH and I so they aren't near the beds edge. I've woke up many times to find I've got one of my feet supporting me on the floor so that I don't fall out. It is amazing how much room a 4 lb Yorkie thinks she needs to sleep.

They can curl up into the tiniest little balls during the day to nap, but come night time they apparently have to stretch out full length crosswise on the bed. If we could get them to sleep in the same direction as we do it would be a lot more comfortable.