Women's tri suit. S/M size 10/12 wanted to buy

[LMitchell]

I'm doing my first triathlon in 3 weeks. I think a tri suit might be something that some people have knocking about at the back of a wardrobe and might prefer ?20 in their pocket and a clearer wardrobe...

I'm size 10-12 in clothing so reckon small or possibly medium in tri suits.

I have a wetsuit for swimming, but will be wearing cycling shorts and a sports bar under it if I can't find a suit! Since it's my first tri,I'm reluctant to spend ?60 on a new one (sadly decathlon don't do ladies tri suits) in case it's my first and only triathlon!

Thanks!

Lucy