A proper bed. And I mean the whole thing: frame, mattress, linens, comforter, pillow, sheets and whatever else you need to get a good night’s rest.
If you can reasonably afford to spend $500, spend $500. If you can afford $1,000, spend $1,000.
When I moved to Munich, I decided to get the same bed from IKEA I’d had before. I brought my mattress on the first day, which is also from there. They make decent ones by now, with softened springs inside or foam.
For the first few days, I slept on the floor, but on a good mattress nonetheless.

Then I started assembling the frame for my bed…

…and the slatted frame.

I feel I sleep even better in it, because I’ve assembled it myself. Must be a psychological twist, but it works.

If you live to be 90 years old and sleep 8 hours a night, you will have spent 30 years in bed.
A third of your life is not something you should cheapen out on. Don’t sleep on sleeping!