A quiet call and easy to blow? Here is some food for thought. A call should be loud, quiet, and easy to blow all in one. Now, easy to blow is very relative. Is it easy to a comp caller? Even poorly made calls sound good in the hands of a good caller. Previous advise about shaving is part of the answer. And yes, sand paper or razor blade, same result. I sometimes use both on the same reed. The other part of the answer is to make sure you are tuning the call correctly. If you do not have experience with this, then hit up Youtube. Plenty of monkeys on there tuning calls. Then destroy about 50 reeds or so.
And still another part of the answer is to try different guts in your call design. Internal dimensions of the barrel greatly effect how easily a call is played. Some guts work well with some dimensions and not so well with others. I have two different call barrels and they play different kinds of guts better or worse than the other. This is a longer process with experimentation, much like duck call tone boards.
Now, the soft or quiet question. Wood typically carries a softer tone than plastics. However, you can get wood pretty dang loud. Also, in the hands of an experienced caller acrylic/plastic can be quiet and soft. No right or wrong answer I suppose, but if someone were to ask me about a good material for a soft and mellow goose call. I would say olive wood. I have heard mixed feelings on this stuff, but some of the sweetest and mellowest calls I have made were from olive wood. It has a very rich tone to it.
I hope this helps a little and doesn't confuse the issue too much.
