The morph tool is fine if you aren't trying to be fancy, e.g. just to pull the fabric out. Bring down the magnitude (the default is way too high and you will overdo things), use a softer brush, pull a little bit many times instead of a lot once, check your work from multiple angles as you go (the posing camera is usually best here). Sometimes Pull is better than Loosen, move the camera around so you can pull the right direction. Smooth can help too although sometimes you need to fix fit after smoothing. I think the morph tool is pretty good actually, but you do need to get a feel for it. You'll only get that feel by using it. Start with simple tasks and work your way up.

The stretch lines are harder, but depending on the scale you want you might be able to do those with a displacement map instead.