Help!

So, here's hoping I may get a suggestion or two on here.

I want to make a sweater. Yeah. I know it's spring. The pattern I'm eyeing (and I'm betting it will take me a few months to make. Can't neglect my secret pal once I get cracking on miles and miles of 2-by-2 rib) calls for Gedifra Cotton Merino. I can't find it, let alone afford the 16 balls I need. So, I'm looking for a substitute.

I think the cotton merino is an aran weight yarn, roughly 50-50 wool to cotton content. So far the other yarns I've found have been 80-20 cotton-wool, and they've been DK or worsted weight. Any suggestions?