My little 3 pounder, Billi sleeps with her dad and I. She has ever since we felt she was fully potty trained. Since we have ramps for her, she can get down from the bed on her own and go potty on her patch and get food/water when she wants. It's actually really satisfying to hear her get up in the middle of the night and take herself to the potty.
As for her falling off the bed... Nah, I wouldn't worry about that. It really depends on where they prefer to sleep anyway. If they're by your feet, have them sleep in between you and your spouse. Sometime's she'll wiggle up behind my back and I can feel her dad roll over and so I'll move so she'll go with me. She usually moves on her own anyway, but it's still strange how aware we always are of her when she's with us.
Idk, it's just something you'll both get used to and you'll find that they're sturdier and fully capable of moving themselves out of the way if you do move around in your sleep a lot. I'd try it out a couple nights and see how you both like it. You never know, maybe he'll prefer to sleep elsewhere anyway.
__________________  [I] Dani: Happily owned by Billi-Jane & Witten 
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