For those that have knit a baby blanket using their own design, I need some help. First of all, I've waited until the eleventh hour to start this blanket, and I need it done quickly

I bought some worsted weight yarn, and I
think I know what kind of design I want to do (could I be any more disorganized with this project???), so here's my questions:
(1) Have you double-stranded or single-stranded your blanket? If you double-stranded, was a too bulky?
(2) What size needle did you use to give the blanket a nice drape? I think my yarn calls for a size 8 (5.0mm) needle.
Thanks!