I am 100% sure that total abstinence is not moral in a marriage.
1 Corinthians 7:5 Do not deprive each other of sexual relations, unless you both agree to refrain from sexual intimacy for a limited time so you can give yourselves more completely to prayer. Afterward, you should come together again so that Satan won’t be able to tempt you because of your lack of self-control.
You may feel 100% sure, but you are mistaken.
There are situations which might require abstinence within marriage. That passage you quote from St. Paul says not to deprive each other, but notice what he immediately follows with “unless you both agree”. He is describing periodic continence. Today there are family planning models that use periodic continence (abstinence). It is permitted to use periodic continence if pregnancy must be avoided, rather than strictly using periodic continence for prayer only. For some serious reasons, total abstinence might be necessary. The writings of the Church Fathers reflect this understanding of marital relations. For couples who were in a position of needing to avoid having any more children, they were advised to abstain. Contraception was always forbidden, all the way back to the beginning of the Church.
Kefla was right that NFP is not absolutely certain to prevent pregnancy and that no one is required to use it. She is also right that you really need pastoral direction to be able to manage the challenge that your wife’s medical condition is to you and her.
But everyone else here is telling you the truth: that there are only two morally licit options, both using some amount of abstinence, either abstinence until her medical condition changes or is managed or she reaches menopause OR periodic abstinence using an NFP method.
Whether you choose to follow the teachings of the Church is still your choice. But seek out the actual teachings, and seek out counsel from knowledgeable people.
Here are a few links to get you started.
The National Catholic Bioethics Center
ncbcenter.org
The Way of the Lord Jesus, by Germaine Grisez, a moral theology work for modern Catholics
twotlj.org
Humanae Vitae, by Pope Paul VI, a letter to Catholics on the various forms of birth regulation, and which forms are moral and which are immoral
w2.vatican.va/content/paul-vi/en/encyclicals/documents/hf_p-vi_enc_25071968_humanae-vitae.html
And one last one that I found extremely helpful when I was learning about the Church, especially with explaining how to navigate questions about marriage and sexuality is the
Catholic Education Resource Center
catholiceducation.org/en/
They have a searchable database of educational articles as well as topical categories that you could choose from and just scroll through and start learning.
I hope these links help you! God bless you!