Contracepting is a gravely evil act. Like all grave evils, in order for us to have a mortal or even venial sin on our conscience from them we must have full freedom to act otherwise. That might not be the case for every individual and you should discuss it with your spiritual director.
This teaching is hard for many to accept, but no harder than teachings that homosexuals may not be sexually active with each other. Consider that many married Saints chose to live in Josephite marriages in service to the Lord. Consider also that your marriage may or may not survive either NFP or a Josephite marriae and what is best for your family. Living a faithful life of service is not intended to be easy:/
Consider also that Jimmy Akin once claimed that saving up for a goal like finishing school or something is not sufficient reason to resort to using NFP and that NFP is not intended to be a long term thing, users who opt for the method should consider their decision every month to determine whether they still have a serious reason to avoid pregnancy. Using NFP without serious reason is also an evil, it is something that might be resorted to but not without sincere soul searching.
Personally, we practiced NFP diligently and had 5 kids in under 8 years (the last 3 while trying to avoid) and my wife prayerfully considered having her tubes tied and went through with it. I don't judge her for it and she's at peace with God over her decision, so I'm okay with it.
Should you choose to practice NFP, know going in that the claimed 99% effective rates need to be taken with a very large asterisk. The German study that found that result rejected women with difficult to interpret fertility signs, uncommonly short and uncommonly long cycles and a few other not-unusual circumstances from participation. It is somewhat akin to saying that 99% of women can run a mile in under 8 minutes, but women over 120 lbs, under 16 years of age and over 30 years of age are excluded.