Quote Sorceress-Eiva:
Can I just start by saying omg, I love you for giving Helena a shot.

Fabric choices... whatever looks good. I pick my fabrics by comparing them to an image of the character and thinking if it would look the same, worse or better in real life. Try to go for something as similar as possible (durr durr I'll stop giving 100% obvious tips now). I wouldn't go for anything shiny, though - shiny materials tend to crease easily and look bad in photos (especially ones taken with flash, which happens at events), not to mention it's more uncomfortable than say, cotton. Don't forget that you're gonna be walking around in this costume for at least a couple of hours, so bear that in mind as well (will you become unbearably hot? Will your legs/arms/etc chafe against leather? Allergies? Etc).

I tend to use either natural or synthetic cotton in my costumes unless it's a particular material that I need (i.e. patterned, sequined, etc) and I've never really had a problem with it, but go for whatever you're comfortable with and can afford. As with anything, better fabrics will cost more!
Hope I've been able to help in some way or another, and good luck with Helena, I can't wait to see how it turns out! <3

Quote limegreenjelly:
you could use leatherette, its got a matt but shiny sort of finish, however it is hard to sew...

Another fabric could be matt lycra, its not shiny, and it will give the appearance your looking for as it tight fitting, and using a zig zag stitch is pretty easy to work with...

You can get patterns for cat suits which are easy enough to find in a simplicity pattern book

Hope this helps

Limegreenjelly x