Re: hitting the cervix
There was another couple who had the same issue, and the suggestion was made that the penis be held with one or a few fingers around it at the base, so as to not push more than could be accomodated.
I think other solutions could be tattooing the base of the penis, to know how far to push it,
or maybe wearing a ring on it, to gauge how far in to put it.
About hitting the cervix, my partner didn't seem to like it either ( it only happened in certain positions when I really pushed ).
I guess your boyfriend should just go slow or practice being precise ( when thrusting fast )
If you want him all the way in because you want him up against your pubic area, then
it might be possible if he mounts you lower, and at an angle close to you ( as opposed to like ninety degrees to you ).