Not petite myself -- but keep in mind the regular sizes here tend to run smaller anyway.
Boy do I disagree with this statement. Everthing runs big here, to me. Most stores don't even carry less than a size 8, which I can't wear. I have only found Next to carry a 6, which only fits half the time. It is ridiculous.
To the OP, Next has a petite line, which is pretty decent. Plus, Next will order whatever size you need and have it delivered to the store. Love that!!!! Debenhams does some petites, but I have trouble finding the petite section in my Debenham's. They move it around a lot.