We will appear in the afterlife in a recognizable form such that those who knew us in this life will recognize us there.
However from narrations it can be deduced that those who go to heaven will be in a more idealized form (for instance, youthful or full of light) and those who commit severe sins may see those sins manifested in their physical form in their bodies.
(Perhaps this is similar to how when we see someone in real life whom we haven't seen for decades, we can sometimes still recognize them even though they look different; there is something about the essence of the person that we recognize rather than the purely physical appearance.)
Whether it is ideal or not to be fat is of course cultural since in some cultures it is/has been considered a mark of beauty/handsomeness and in other cultures it is not. But what can be said is that the way the people in Paradise will appear will come across as positive, regardless of the details of what the actual appearance is.