I think the idea of plush walls is great! I wish i could plush my whole house. Cooper sleeps with me. He's 9 pounds so it's pretty easy to know where he is, which is usually across the bed
My little Max is almost 5 pounds, but as soon as he's potty trained he'll be in the bed too.
I would definitely consider getting steps to let the royalty know how to get on/off the bed safely.