Prayer Shawls?

There's a small group I'm joining who prayerfully knit or crochet prayer shawls, and I thought I'd try crocheting for their purpose. This is going to require purchases; I spent a couple of days hauling out my complete collection of crochet needles but I never handled anything as apparently large as the ones they specify -- size "M", size "P" ? I took a skein of wool from last winter's barely started scarf, and unraveled it to see what my own largest needle would produce. One conclusion: the pretty rippled yarn makes it pretty hard to see the crochet stitches, for someone who's more used to hard tight string-like crochet. I remember the knitting was effortless, it's a good yarn, but I guess I don't have enough of it, anyhow.

So I'll have to consider buying before I have much idea what to buy. Maybe I'll get big needles today, and try some of my other old skeins for samples to see what it looks like? Yes, I wish you were here to coach me. I hate to get truly started on something that won't be what I eventually would want...Advice?