I used to do stuff like that when I was a kid... only I created a dream story to enter.
Just get a standard voice recorder and record your message into it and then play it when you go to bed.
I always filled the first 20 minutes or so with relaxing music to help me fall asleep and then I recorded the story.
Just search the web for inspirational/motivational sayings and record those in a relaxing voice.

Tell us how it goes.