Hi, welcome to KH. Choosing the best scarf yarn is very subjective. What would be best to one person would not be best to another.
There are some very soft acrylics. Caron's Simply Soft is one a lot of people like but there are others, and the price is not high.
There are some acrylic/wool blends that are quite soft and have a little more feel of wool, Wool-Ease is one I can't think of anymore names right now.
There are on-line sources of cheaper wools like KnitPicks and Webs. I actually think that to be sure it is soft around the neck, a soft acrylic or a blend would be a good place to start. The really soft wools can be more expensive.
For your needles you would want a worsted weight (#4 if you find the numbering system used) and if you are a new knitter I suggest something smooth (not hairy or weird in any way
)yarn in a medium to light color. Black and very dark yarns are harder to work on.