A volume with different curves

Diff the part to taper

here I kill the Top / Bottom faces + one face of the no Tapered part (not indispensable - its just for see the internal volume :)
Separate
Show Points for easy selection of points who will "scaled"
Scale 1D on the Height by a middle
Scale 1D on the Width by a middle

NetWork Top / Bottom
Join All
= I have a Solid

Follow 2 "tapered" from different start face