Help me fix my slouchy sock please!

[joshs_girl]

I've got one of the Monkey socks done. However, it's kind of slouchy and falls down a bit after a few minutes of wearing.

Should I just add more ribbing at the top? Right now, I have seven rows of k3p1 ribbing.

Should I go down a needle size as I get closer to the top?

It's Collinette Jitterbug and I'm working it on size 1s. Because of the pattern, I can't really decrease any stitches. The yarn feels kind of heavy and stretchy - so is the yarn part of my problem?

[amey]

On the most recent pair of socks I knit, I did the ribbing in a smaller needle size - just about 1.5 inches (the rest of the leg was plain stockinette). THey feel snugger than the ones where I've used the same needle for ribbing as the rest of the sock.

Oh, and I did the socks on a US1.5 (2.5mm) and the ribbing on a US0 (2mm).