It is objective moral truth, regardless of how well people are able to live in accordance with it. And the prohibition on deliberate subversion of the human sexual configuration is very logical, and also very clear.
To reject it as the foundation for morality is to reject nearly all of the Church’s teachings. It is practically to reject God, who ordained the natural order and who sustains it in every moment that it is.
No. The only sane, logical, and moral thing to do would be to refrain from further sex until your natural fecundity has run its course. It would, in fact, be outrageously immoral to subject yourself to such risk just a few paltry orgasms.
At any rate, the issue is not whether or not you will die for having more children (unless you added new info somewhere that I missed – I have not kept up with this thread very carefully); as you said, the issue is that you want to travel and have a career and so on and you cannot reconcile this with your marital duties. If your marriage suffers, it will be solely because you have elected to prioritize your worldly ambitions and desires and dreams over the duties to which you committed yourself, not because of the Church’s (morally legitimate) prohibition on contraception.
The prohibition on sterilization does not stem from the relative complexity or simplicity of the procedure. It does not exist to make your life easier or more difficult. The God of the Church is not the God of your earthly wants or your material well-being or your sexual satisfaction or your personal convenience. He does not care if you get the chance to write a book or see Europe. He cares if you get to see Him, forever, in Heaven. Any assertion to the contrary is a flimsy rationalization.
The course you are contemplating is contrary to natural law; it is impiety against the Church, which has a legitimate basis for its claim to truth and which commands your deference; it risks scandalizing your husband if he consents to it and it compounds the sin with dishonesty if you do it behind his back. It is folly piled upon folly, and I cannot strongly recommend enough that you rethink your position, since it seems to me that you are pretty intent on embarking on it regardless of what anyone here says.