Hello egyptianprincess before I post I should say that I am a little biased in that that I had a severe tear with my DD and have opted for a vb against medical advice.
I think you can ignore the baby's weight, I don't think it is a huge risk factor for tearing unless combined with other factors (baby's position, first baby, episitomy, epidural, instrumental delivery and I think induction but I am not certain).
Have you done any pelvic floor exercises post natally and during pregnancy? You should be doing about 100 a day post natally and less in pregnancy but still some (about 10 I think). The main thing to weaken the pelvic floor is pregnancy so provided you are free to move about and birth in a position your body is comfortable in your minimise your chance. The riskiest position for tearing is on your back because you are pushing the baby up through your perinuem.
Have you looked at breathing and relaxation as a coping technique for labour? They are unlikely to give you an epidural as early as 1cm dilated so you'll need something to bridge the gap if you decide to have an epidural or you may find that you manage just fine with breathing and movement.
CS is not without risks, google them, there is no evidence that CS prevents pelvic floor damage. Did you have any issues with incontinence after your DD's birth? I believe that the NHS offer elcs if you are symptomatic but I have spoken with a colorectal surgeon who says that there is no evidence to support the theory that it will prevent existing symptoms worsening. I guess if you are worried about tearing then that in itself can hinder labour so you may choose to go for the CS.
From experience, an episiotomy was much, much harder to recover from than a tear. I have never had a cs so can't compare that but would recommend you google it so that you're aware of the downsides.
Like I said I opted for another vb. My risk of tearing again is in the region of 5%. The risk of a cut to my stomach with a CS is a 100%. I want to give myself the best chance of enjoying DC2's first weeks.
Sorry, that probably isn't much help. I know it's a hard decision, I hope you get lots of info and come to the best decision for you.