Hi Rosamund – welcome to the forums! Unfortunately I don’t have experience with catheters but I’m so sorry about the pain and discomfort you’ve had, it sounds miserable. There are some excellent doctors in these forums that might be able to help on those particular questions.
As to your issues in general with past painful pap smears, do you have a doctor/gynecologist you trust to work with? I’ve found that with my vaginal pain issues, having a supportive and understanding set of medical professionals was the thing that finally helped me (and that people who DIDN’T understand my pain made my shame and feelings of differentness even worse). If you don’t have a specialist you like, HOWEVER you decide to tackle this, I recommend calling around and seeing if you can find a doctor or gynecologist who is familiar with vaginismus, vulvodynia, or female sexual pain in general. Even if you aren’t suffering from one of these exact issues, a practitioner who is familiar with them will likely be more sympathetic and patient and will care more about your experience if you do need a catheter or other device implanted.