Yes, the Crew sleeps between us in the Valley of the Giants. If we don't let them up (by setting up the doggie stairs) they will let us know about it - loudly.
We have a new bed, and these are high. You have to get the doggy staircases or at least a big stool with one of these.
One of our friends had a Yorkie that had to be put to sleep because it fell out of bed and broke its back, so there certainly is a risk. How do you mitigate this hazard? Like other posters have noted - MAKE SURE the Yorkies are sleeping in the middle. Also, we bought a giant dog bed (its giant for Yorkies, that is, it’s just a normal big dog bed with lots of cushion). We move this big bed each night from their look out post at the top of the stairs to right next to the bed on the side they would be most likely to fall from if they were to sneak away from the valley.
Can little dogs get smothered like babies with SIDS? I don't know. I do know that we have had Yorkie(s) sleeping between us for many years without incident.
If you start this habit, its hard to stop! Also, it can be detrimental to getting a good night’s sleep, even though overall I like it a lot. What I mean is they are HOT, and in the summer I really don’t want them curled up next to me, but they sometimes have other ideas. Also, you should be constantly mindful of their location, and you have to be careful when you flip, hard for guys who move around in their sleep (more than women, so I have read).
Other advantages? Ours lick us in the face when they have to pee

