Check out the Mn Camping Board!
SIMs are self inflating mattresses and have a layer of memory foam within them. The 'self inflating' property is because when you unroll them and undo the valve air rushes n and puffs up the squashed foam. No pump needed.
These mats are very comfortable for many, Decathlon do ones which are easy to pack down (rolling up a double SIM is hard work IMO - and I would get 2 singles if you go for this option)
SIMs are insulated against the cold in the ground. They are harder to puncture as they are nt made of simple plastic like air mattresses.
Then there are blow up beds. Traditional air mattresses, that you fill with air from a pump and some come with a built in pump - confusable with 'self inflating'.
Blow-up mattresses are much cheaper, puncture more easily, will need topping up as air gets colder at night, and also offer no insulation form the ground - they are a bag of cold air. Best with some insulation underneath or on top.
Whether people prefer blow up beds or SIMs for comfort varies widely and is very individual.
I would see if Decathlon / Go outdoors have displays where you can test them out.
I hate blow up beds as they just generally sink into the heaviest point, whereas a SIM squashes down according to your contours, iyswim.
I am v happy on a 10Cm SIM - and was on my 7.4Cm one, too.
Kids don't need such thick SIMs as they are lighter and don't squash them down as much.