DIY Puppy Step Stool

I love my little dog, but he has some annoying habits. Every evening, when I'm getting ready to sleep, he asks to climb up into my bed. I help him in and we fall asleep together. Then, in the middle of the night, for whatever reason, he'll get up and leave. I don't know what he does because I'm asleep; I suspect either going for a wee or a drink or maybe to play with toys. Actually, sometimes I