A culture can be known for varying degrees of sleep, which the species/race makeup of that society can impact. A race that needs little sleep might have an active nightlife. One that needs a lot might have afternoon naps as commonplace. If that race dominates the culture, the impact will be felt. If it does not, then other races may judge them for how much or little rest they need.
In many Earth cultures, it’s standard for a couple (especially if married) to sleep in the same bed, but that’s a custom. It isn’t necessary. Consider keeping this in a society with low temperatures much of the year; in Game of Thrones, some women are referred to as “bed warmers.” This is unlikely in a hot climate and people may prefer their own beds, which don’t need to be in the same room, either. Imagine a race where the males always snore; the females may be used to it, or they may insist on different rooms.
Some other questions to ask are:
- Do children sleep with their parents, either in the same bed or room?
- What age is this frowned upon, if ever?
- Is the culture aware of Sudden Infant Death Syndrome and preventing it?
- Do babies have traditional items slept with, like a teddy bear? We can mock an adult character who retains such an item or simply has one around for some reason, such as intending to give it to a niece.
- Do people sleep with a light on or total darkness? Perhaps a scented candle is traditionally lit on some occasion. If the environment is typically bright or daytime naps occur, maybe masks are worn just then or all the time.
- Do window coverings exist because of this and allow for easy manipulation?
- Do people sleep nude, in undergarments, or specific bed clothes? Naturally, regional air temperatures influence this.
The shape of beds is assumed to be rectangular due to our bodies being longer than wide while lying down, so no one will question this. But we can imagine that a bed for two does not anticipate them lying side-by-side. How about feet-to-feet, or head-to-head, in a very long bed? Circular beds are an option, as are those inspired by a culturally significant symbol, such as a heart for a honeymoon suite. There are also bunk beds, water beds, air beds, pods, ones that can be retracted into a wall, those on the floor (without legs), or even suspended ones, like a hammock. Something is likely to dominate. Decide what it is, what’s traditional, and what’s the latest craze. Don’t forget to mention those useless, decorative pillows, should they exist.