There are fourteen weeks until Christmas, which sounds like plenty until you remember that the spare room is currently holding a clothes airer, two boxes of decorations and a bike. Of all the rooms in a house, it is the one guests remember most clearly, because it is the only one they are left alone in.

The good news is that a guest bedroom does not need much. It needs a bed someone can genuinely sleep on, somewhere to put their things, and about four small touches. Here are the guest bedroom ideas that actually change how a night in your spare room feels.

Start with a bed people can sleep on

The single biggest improvement most spare rooms can make is replacing the sofa bed with a real bed. Sofa beds earn their place in a studio flat or a room that is genuinely a second living room. In a room that is used as a bedroom three or four times a year, they are a compromise nobody enjoys: a thin mattress over a metal frame, and a bar in the wrong place.

A proper divan set costs less than most people expect and does two jobs at once, because the base can carry drawers. Spare duvets, winter bedding, the pillows you only need when four people stay — all of it goes under the bed rather than into a cupboard you do not have. If you are weighing up bases, our guide to divans, ottomans and bed frames covers the differences.

On size: a double at 135cm wide is the sensible default for a spare room. A single works if the room genuinely cannot take more, but it rules out couples, which is most of who stays at Christmas. If the room is tight, a small double at 120cm is worth knowing about — it takes 15cm less floor and still sleeps two.

What mattress firmness suits someone you do not know?

This is the question we get asked most about spare rooms, and the honest answer is that you cannot get it exactly right, so aim for the middle.

A medium mattress is the safe choice. It suits back and side sleepers, it does not punish anyone light, and it does not leave anyone heavier sinking. Firm mattresses divide opinion sharply and soft ones divide it further. Medium is the one nobody complains about, which is precisely what you want from a bed you are not sleeping in yourself. Our mattress guide goes into fillings and support if you want the detail.

One more thing worth doing: actually sleep in the spare room for one night before December. You will find the things guests are too polite to mention — the landing light that shines straight onto the pillow, the radiator that ticks, the door that does not quite close. Every one of those is a five-minute fix once you know about it, and none of them get reported by a guest.

The spare room is the only room in the house your guests are left alone in. It is the one they remember.

The four things that make a guest room feel considered

None of these are expensive. All of them get noticed.

• A bedside cabinet and a lamp on each side. Not one — each side. Nothing says "this room is an afterthought" more clearly than one person having nowhere to put their phone, their book and their glass of water. Bedside cabinets with a drawer are better still.
• A mirror. Guests need somewhere to get ready that is not your bathroom, particularly if there is one bathroom and six people. A full-length mirror earns its wall.
• A chest of drawers with two empty drawers. A chest full of your own things is storage; two genuinely empty drawers are hospitality. Anyone staying more than one night wants to unpack.
• A clear surface. One place to set down a suitcase, a book, a cup of tea, without moving something of yours first.

Somewhere to put a suitcase

People underestimate this one. A suitcase that has nowhere to go ends up open on the floor, which turns a tidy room into an obstacle course by the second morning.

A stool or a blanket box at the foot of the bed solves it, and doubles as a seat for putting shoes on and a home for the spare blanket. Leave about 75cm of clear floor down at least one side of the bed so nobody is edging past it in the dark, in an unfamiliar house.

Warmth and blackout

A spare room is usually the coldest room in the house, because the radiator has been off since March and the door has been shut. Turn the heating on in there a day before anyone arrives, not an hour.

Beyond that: an extra blanket or throw folded at the end of the bed, so nobody has to ask; and curtains that genuinely block light. Highland summer mornings start unreasonably early, and while that is less of an issue in December, guests come in June too.

The other winter detail is condensation. A room that has been shut up for months, then slept in by two people for three nights, will show damp on the window by the second morning. Leave the door open for a few days beforehand so the air moves, and the room will smell better as well.

Guest room essentials: the night-before checklist

Assuming the furniture is right, everything else is a ten-minute job the evening before someone arrives.

When the spare room is also the office

Most spare rooms in the Highlands are doing two jobs, and the second one is usually work. That is entirely workable, as long as the working half can be switched off.

Put the desk or console under the window and the bed on the opposite wall, keep the office storage behind closed doors, and clear the desk surface before guests arrive. Our piece on home office ideas covers the furniture side of that in detail.