When I moved into my flat I had to give away my very comfortable double divan which had been in my spare room in the house, as there really was not enough room in my (now) spare room to keep a double bed made up in there.
So, then I was looking for a sofa bed. Needed one that would also be easy for me to pull out into a bed, and pack away.
Choosing one is dependant on the space you have. My eldest daughter fitted out her smallest bedroom for me to stay in when I am in London. Hers comes from Ikea and has storage in it for duvet and pillows and bedding. It pulls out sideways which is right for that room,.
In my spare bedroom I needed one that pulled out forward '(like the old-type 'put-u-ups'. I also wanted one that did not have arms when it was a sofa, to save room. I had brought two nice narrow bedside tables with me and wanted to be able use those. Also wanted one that opened to (or as near as possible) to a full 4'6" double bed. Did a lot of research and finally found one which fitted all of these criteria in DFS.
As with all sofa beds, think they work better with a really high quality mattress cover under the sheet when made up as a bed.
Do check that fitted sheets will go on this as a bed, some have no where to slot the corners over.
You really need to do a lot of research. Are the looks of the sofa of great importance? How much room do you have both when closed and when pulled out? Do you want one that pulls out sideways or forward? Do you have other storage for bedding? As with anything, the more you pay the better it is likely to be. My one cost me around £800. jut over two years ago. Guests have said it is one of the most comfortable beds they have slept in.