Corriedale wool slivers are wonderfully bulky and can be needle felted on their own or used as a cheap and cheerful top coat over core wool. They also work very well for 2D work.
With the exception of ‘Eggshell’ they come with a degree of variegation in their colour which provides added interest without having to blend colours.
If needle felted directly for 3D work they retain a good degree of bounce if that is what you’re after but can be felted flat as a top coat over core wool.
They can of course also be spun or woven or used for other crafts