HSV1 and kissing

In general, the chance is low--think how many people kiss others and how ofthe that happens, and how few of those events result in herpes transmisison.  As you suggest, if one person is infected and the other isn't, the odds are higher with french kissing than less intimate forms of kissing; and the odds would be higher if the infected person had recently acquired infection compared with chronic infection.  It isn't known whether the transmission risk is higher from symptomatic lesions vs asymptomatic shedding.  (For genital HSV-2, there is littleLittle noses decongestant
Little tummys or no difference). might be higher when overt lesions are present (but maybe not); and so on.  About half the population is infected, meaning there is a 50:50 chance you already have HSV-1 yourself--in which case, your chance of getting a new HSV-1 infection is virtually zero, even if exposed.

The risk of STD transmission by oral contact with breast (or any other skin surface other than the genitals) must be just about zero.  In 30 years of working in a busy STD clinic, I have never seen or heard of a case.  In distant decades, once in a while a baby would get syphilis from a non-maternal wet nurse.

Good luck--  HHH, MD