Substituting Yarn in Pattern

Hi Everyone, I know close to nothing about knitting but I am having a friend knit something for me. I’ve selected a pattern I like but am wondering if I can substitute the yarn called for with the yarn I would like.

Pattern: Calls for 3 skeins of 138 yard, 50g, 100% bamboo yarn. That’s about 420 yards of yarn weighing 150g. The gauge, as far as I can tell, 30 rounds at 25 stitches for 4x4", on size 4 needles.
Link: http://www.interweaveknits.com/freepatterns/pdf/spr_07/Lace_nightie.pdf

Yarn I’d like to use, Superior by Filatora Di Crosa, 70% Cashmere, 30% silk, 6 stitches per inch = 24 stc/4", on size 4 needles (I think). A separate review at Knitter’s Review said 30 rounds for 4" is about right on size 4 needles. Comes in 330 yard skeins, each weighing 25g. 420 yards would be roughly 31g.
Link: http://www.tahkistacycharles.com/dyn_prod.php?p=SUPE&k=73694

I’m under the assumption that gauge will determine the sizing/look of the item, and that the gauges here match… am I correct?

Having the exact pattern/detail is not important to me.

The major difference is the weight difference; 150 grams vs about 30 grams. Is that a problem? I know that the garment will obviously have a different feel and drape differently, but that’s what I am looking for. Will the pattern work, will the result look ok, with the different weight?

Next, after matching the gauges, do I simply need to buy the same amount of yarn the pattern calls for? In this case, the roughly 420 yards?

Is there anything else I should consider, besides Gauge, Weight, and Yardage?

Thanks everyone in advance for your help!

The gauge is the most important thing for size, and that the yardage is about the same.

The weight differs so much because bamboo is rather heavy in weight, and the yarn you picked looks very lightweight.

The nightie will most likely be a lot more sheer with the yarn you chose, but mmmmmmm, it should be soft!

Thank you Ingrid, it should work fine, my gauging and sizing is correct?

Thanks again!

If your knitter gets the proper gauge, then the size should be fine.