Yes, there are differences in needle sizes. Here's a chart so you can figure it out.
http://www.fibergypsy.com/common/needles.shtml
This is a standards for yarn that will help you figure out what yarn you have. 4 ply doesn't really help. We need the yarn weight (worsted, DK, etc).
http://www.yarnstandards.com/weight.html
Now, not knowing what weight your yarn is here are a few patterns that have v-necks.
http://thecompletefabrication.blogsp.../09/felix.html
http://knitlist.com/96gift/giftlutzlingsweater.htm
http://sasw.blogspot.com/2005/03/baby-cardigan.html