For the following, I strongly recommend that you pay attention to their respective Neutral (or Neg) reviews on here:
petiteamanda1994
Lovely@Melissa!xo
Katarina Weiss.
As for Helena's adventure - I don't think she's offering sex anymore, preferring to focus on tantric massage at £200.
Valentina Italiana, I seem to recall had a hilariously-written, but ultimately damning review from a respected member on the London board. When she had a different profile. She managed to talk for two hours without any sex occurring.
Don't know about the others...
Best luck