If you do go for a camp bed, go for one in the style of the first argos link you gave. That is a copy of the US army 'cot bed'- and is a big improvement on the older british style ones with the thick wire legs under tension. I've used both (well, the army issue versions), and really there is no contest. You can sit on the side of the us style ones as well without it flipping up unlike the british ones!
The british army now issue the us style beds, and you can even get a mossi net frame to clip onto them. As mentioned above, best combine with a sleeping mat to provide insulation, and you will need something to stop the legs risking puncturing your tent groundsheet. If you can, try to find a genuine army surplus version- they tend to be better quality. I've seen cheap civvy copies with torn fabric.