I recommend MicroSpun by Lion Brand Yarn. It is a sport weight yarn and very silky soft feeling. I love it. The gauge on it. using size 4 needles is 24 stitches in 4" and 32 rows in 4". There are 2.5 ozs in a skein and it is 100% microfiber acrylic.
If you use a crochet hook with it the hook size is H-8 13 sc in 4" and 16 rows in 4". There are 168 yds or 154 meters.
It is machine washable and dryable.

If the purpose of the sweater is to keep someone warm, MicroSpun might not be the right choice. It is very soft, the drape is excellent, but it does not make a warm garment, and it does have a tendency to split.

daylilydayzed is right in steering you towards a sport weight yarn. I have had excellent results with Bernat's Satin Sport, but there are many brands available.

Good luck with future projects!

I like Encore DK--lovely to work with, not too heavy but still warm. And it's washable.

Annie