How does caesium’s density change with temperature?
Looking at the wikipedia page you can see that the density is $\rho=1.93$ kg/l at room temperature and $\rho=1.843 kg/l$ at it's melting point.

Additional information can be found in this paper, where they experimentally explore the density of liquid Cesium in the vicinity of its melting point. In the range of 302 to 375 K to be exact.

From their experimental data they deduce the following approximate equation for the density as a function of the temperature:
$$\rho= 1829.12- 0.61483 \left(T-T_{melt}\right) $$
where $T_{melt}=301.6$ K.

This shows that the density reduces with temperature. Plotting the information that we have from the paper and from wikipedia yields:



The jump at the melting point is from the mismatch between the paper and wikipedia. In the paper they specify specifically that the density is for the liquid case, on wikipedia it might (I'm not sure) be the density for the solid case at the melting point. If that is the case then the jump in density from solid to liquid is: $1843-1829=14 $kg/m$^3$