The size of a mattress can affect the overall feel and comfort of the bed, but it is not the only factor that determines how a mattress feels. (pretty much not true except with mattresses that have a very firm foam encasement around the perimeter. With this type of mattress in a twin or twinxl size you have to sleep close to or on the firm foam encasement and you may well notice it)
The type of materials used in the construction of the mattress, the firmness level, and the support it provides can all contribute to the overall feel of the bed. (This answer is laughable because the listed qualities are all that matters)
So while different sizes of mattresses may feel different, it is not necessarily because of their size alone. (99% incorrect because it can almost never be because of the size difference)
It is important to consider all of these factors when choosing a new mattress. (True but pay the absolute least attention to size differences)