According to Humane Vitae and the catechesis there is nothing wrong in using NFP if you for a good and unselfish reason cannot receive more children. However, I often get the impression that if you want to be really holy as a married couple, you should stick to total abstinence when you no longer have the intention of receiving more children (as for example the beatified couple Luigi Beltrame Quattrocchi and Maria Corsini did).
And even if total abstinence isn’t officially proclaimed to be the ideal way of living for couples who for just reasons do not want to receive more children, are there any church documents or theologians that say that NFP (that is, intercourse during infertile periods within the limits of just moderation) could actually be better than post-children celibacy? Theology of the Body, or Christopher West, perhaps?
Humane Vitae and the Catechesis says this:
And when the infertile period recurs, they use their married intimacy to express their mutual love and safeguard their fidelity toward one another. In doing this they certainly give proof of a true and authentic love. (Humane Vitae 16)
The Creator himself . . . established that in the [generative] function, spouses should experience pleasure and enjoyment of body and spirit. Therefore, the spouses do nothing evil in seeking this pleasure and enjoyment. They accept what the Creator has intended for them. At the same time, spouses should know how to keep themselves within the limits of just moderation. (Pius XII, Discourse, October 29,1951, quoted from CCC 2362)
I have also found this quote from Fulton Sheen’s “Three to get married”:
When husband and wife live their married lives as reflections of
the Divine Prototype, their relations one with another become a
source of merit. They save their souls through union with one
another. Sacramental grace is communicated in the marriage act.
And also this article which I am unsure of its origin that says:
If marriage is in itself a divine way of holiness, then all of its natural elements, including of course intimate conjugal relations, are a matter of sanctification. Certainly (as we will see below) these relations must be marked by temperance; yet total abstinence from such relations cannot be proposed as an ideal or ascetical goal for married people.