A sofa bed has two jobs, and most people have a clear favourite. In a living room, it may be a sofa every day and a guest bed twice a year. In a studio flat, it may need to become a bed every night.

That difference should shape what you buy. There is little sense choosing a complicated sleeping mechanism for guests who rarely stay. Equally, a sofa that looks lovely when closed is no bargain if its sleeping surface leaves a regular guest uncomfortable.

Before browsing Sofa Beds, decide how often the bed will be used and by whom. Then compare the options on those terms.

First, forget the number of sofa seats

A “two-seater sofa bed” tells you how many people it seats. It does not tell you whether two adults will have enough room to sleep.

Look for the sleeping area’s width and length, measured with the bed open. Do not use the sofa’s overall width as a substitute; arms and framing take up part of it. If you are buying for a couple, this is one of the first figures to request when it is missing from a listing.

It also helps to know who is coming to stay. A bed that is fine for one guest for a weekend may feel cramped for two. If your guests are tall, length matters as much as width. These are better buying questions than whether the closed sofa looks “full sized” in a photograph.

Which type of sofa bed should you choose?

The opening mechanism affects the sleeping surface and what you have to do to get the bed ready.

With a Click Clack Sofa Bed, the back folds down to make a bed. It is a straightforward option worth considering for occasional guests. Because the seat and back commonly form the sleeping surface, pay attention to the join between them and how the cushions feel when flat.

A Pull Out Sofa opens a bed from within or beneath the seat. Some have a separate mattress, which gives you another element to compare. For example, CFS’s Fairfield pull-out sofa bed offers standard and deluxe mattress options. That choice is more useful to a frequent guest than a feature they will never notice when sleeping.

If you need plenty of seating during the day, a Corner Sofa Bed may suit the room. Treat its open size seriously, though. A corner sofa already occupies two sides of the space; the bed can take over much of what remains.

None of these mechanisms is automatically the most comfortable. If possible, open the sofa yourself and lie on it—not just sit on it.

What will happen to the rest of the room at bedtime?

Picture an ordinary evening. Your guest arrives, you open the bed, and the coffee table is still in front of the sofa. Where does it go? Where do the loose cushions go? Can your guest get past the opened bed to reach the door?

Measure the sofa closed and open, then mark its open outline on the floor. Try the layout with your existing Coffee Table in place. If you have to move the table, make sure there is somewhere sensible to put it overnight.

Pay attention to a door that swings into the room, a desk drawer beside the sofa or a radiator behind it. The bed does not have to leave the room looking spacious, but your guest should be able to get in, move around it and get out without an obstacle course.

If it will be your main sofa, sit on it properly

The bed may be used for a few nights a year; you might sit on the sofa for hours each week. Give its seat the same attention you would give any other sofa.

Sit upright and lean back. Is the seat depth comfortable? Does the back support you? Can you stand up easily? Open and close the bed, then sit down again. If you find the sofa uncomfortable in its usual position, a good guest mattress will not make up for it.

The reverse matters when someone sleeps on it often. Ask about the mattress or sleeping surface, whether it is intended for frequent use and what bedding size fits it. Avoid assuming a particular mattress thickness is necessary for every design; a folding seat and a separate pull-out mattress are built differently.

Storage can help, if you can reach it

A duvet and two pillows take up more cupboard space than you might expect. Sofa Beds with Storage can be useful when the living room also has to hold the guest bedding.

Look at how the storage opens. If you would have to move the coffee table to reach the compartment, that might still be fine once in a while. It becomes tiresome if you make the bed every night. Check where you will put removable cushions as well; they need a home while the sofa is open.

Before you settle on a model

Make sure you know the sleeping area’s size, the sofa’s open dimensions and what is included with its mattress. Then measure the route into your home. A sofa bed’s frame may arrive in a large piece even when its final position fits the room easily. Doorways, hallway turns and stairs deserve as much attention as the wall where the sofa will stand. Read the delivery details for the particular model, as arrangements can differ.

The best sofa bed for occasional visitors may be quite different from the best one for nightly sleeping. Buy for the way your household will actually use both halves of it—the sofa you sit on and the bed you open.