Obviously the #1 thing that helps is a nice-fitting diaper. Even better if it has designs.
Babyish objects like pacifiers, toys, blankets, all of that, they help.
If I want to sleep baby-ishly, then my Wave Projector helps, and coupled with that is relaxing music.
Solitudes or 'baby music' on YouTube is the best, especially in long compilations that don't require my input.