The knit garters you buy commercially are knit flat, which I think would help alleviate the "rope around your calf" feeling that piperdh alludes to. I'd say about 1.25" to 1.5" would be a good width to aim for.

Just tell your wife it's like knitting a really tiny scarf. :-)

My wife, who is the knitter in the family, is asleep at present, but without waking her to ask, I would suggest the appropriately named garter stitch be used.