I used this body for Luke:
https://www.monkeydepot.com/Figure_DamToys_Muscle_Body_w_Neck_Post_p/dml1026.htm
It may *seem* large, but it had narrow shoulders and waist.
That model of DAM body is based on the hot toys skinny body HT uses for luke and the only difference(Besides the seamless neck), are the thick thighs. I ground those down a bit with a dremel to make them slimmer, then bound them in a layer of electrical tape(The surface was a bit rough).
The arms are nice and skinny, and all i did other than remove the neck and slim down the thighs(Neck is pvc and can be cut with a blade, see pics below), was to add a little bit of shoulder padding.
As JediJim mentioned above, i slightly retailored the inside seams of the tunic a bit, but otherwise, the costume is untouched. It's all the newer body.
Neck cut(But still in place):
And removed. This is easy to do. Just pop that neck joint off:
Notice how slender the body is. It works perfectly for Luke. If you still reckon it's too bulky, you can remove as much of the chest and ribs as you like. It's just a pvc piece on the plastic body itself:
With the legs cut down a bit, and with shoulders built up a little:
And the final result with the retailored suit.