If you've got £70 to dish out on a petticoat at American Apparel or anywhere else, then go ahead. But, being cheapo, I'm quite happy with a £6 petticoat from the children's section at Matalan. It's a little shorter than I'd have liked (probably at least as long as the AA one though) and it's in a shocking pinky red colour, but it was half price and I'll wear it under dresses and skirts anyway, so I'm willing to compromise.
Also, a new Asda Living opened recently near me. Here are a few cosy-looking things I spotted in there.