When I try to go to sleep, even if my bed is pretty comfortable, I try to imagine myself in some kind of fantasy environment that is even more conducive to sleep and relaxation.
1. Floating in Water/Fluid
I sleep with a CPAP mask, so imagining it like a scuba mask that keeps me breathing while I'm underwater can be a pleasant thought. I can also imagine myself in a Star Wars bacta tank like Luke Skywalker in Empire Strikes Back, and it heals any aches and pains I might have. Finally, if you could be suspended in something akin to amniotic fluid that was breathable, you wouldn't worry about the mask.
2. Hammock in the Shade, by the Beach
3. In a private sleeper car on a long train ride
4. In the arms of a giant teddy bear
5. Riding down a tame, infinitely long water slide
the turns are gentle and undulating so you're rocked like a baby as you go along.
6. Floating in a lazy river
7. In zero gravity on a spaceship
Bonus points for a serene view
8. A sensory deprivation float tank
Of course, these exist in real life. I've got a session booked for a few hours from now.
9. An isolated cave on a mountain top, but with an abundance of cushioning and silk sheets, etc.
10. A padded exoskeleton that provides optimal support in whatever position I am without requiring any muscular or joint effort
It also has nanobots that scratch any itch I feel with nothing but a thought from me.