Lettuce Coat angst

I have cast on for the (Ravelry Link) Lettuce Coat from Custom Knits by Wendy Bernard. I scored the Malabrigo for it in the Red Java colorway (that I have admired for two years but could never afford) at a reasonable price at Webbs. I have only done about six rows, because I am uneasy. The gauge for this coat is 14 st / 4 in on #9 needles. Ball band says 16-20 st / 4 in on size 7-9 needles. I had to go up to a size 13 needle to get close to gauge. The holes are pretty big and I'm not sure that the fabric isn't too floppy for a coat. I swatched over and over, and I've stopped and measured gauge in several places and gone round and round. The problem is, I don't own a size 12 needle. Size 11 gives me 15st/in and size 13 gives me 13 st/in. Problem #2 is, there's a big jump in sizing, I'm a 39" bust, and the sizing is 40" or 43-1/2", which would be too big and bulky in this loose-spun yarn. So I'd rather fall short on gauge and get my size slightly larger than 40", rather than go down to an 11 and have to block the heck out of it. All I can hope for, I guess, is that this yarn will bloom after washing and fill in those big loop holes a bit. It is loosely spun, so should bloom. I know, I know, I should have washed the swatch.

Checked on Ravelry, everyone else used size 9 needles for their coats, and only one person mentioned having to block the heck out of it. So either they used the #9 and knit a larger size, or they have a very tight coat.

Checked on wiseneedle.com, they are saying it's 18 st / 4" on a #9, which makes me feel better using a #13 to get 14 st/ in.

Guess I'll blunder ahead and see what happens.