There are many possible answers. One cannot know what sort of answer is most suitable for your particular application without further information. I will supply one answer that more or less fits your description. In order to avoid confusion with multiplication, I will change your notation slightly, using for example $s_x$ instead of sx, $e_x$ instead of ex, and so on.
Here is a suggested formula.
It is easy to check that this works. When $x=s_x$, the squared term is equal to $1$, and $y=e_y-(e_y-s_y)=s_y$. When $x=e_x$, the squared term is $0$, and $y=e_y$. The fact that I squared ensures that the approach to $e_y$ is rapid at the beginning and slow when $y$ is close to $e_y$. I used the square function as a reaction to your mention of gravity. One can adjust the rate of approach by changing the exponent from $2$ to something else. For a more rapid approach at the beginning, use, for example, $4$ instead of $2$. You can use non-integer exponents, like $1.6$ or $2.7$ instead of $2$ to adjust things so that they fit your application reasonably.