Natural family planning to IUD?

So I’ve been using natural family planning to prevent pregnancy due to issues with birth control and condoms. It’s been about a year and a half.

Just wondering if anyone has done this in a very long term time frame? I’m diligent and know my body well. I use opk’s to see when I’ll be ovulating, we avoid sex for 3 days after a positive opk, we use spermicide on everyday other than the 5-6 days after my period just in case, I temp as well. And idk just getting super tired of doing all this work but definitely don’t want a baby, like ever.

So I’m considering an IUD however my experience with birth control hasn’t been the best. Pills, the shot, the nuvaring, and the patch are all out of the question as I have tried and failed them. So I’m either on to an IUD or the implant. But idk which to chose because I’ve learned the doctors don’t tell you all the risks and possible side effects. So looking for personal stories. Thanks!

Edited to add we don’t want kids due to my health, both mental and physical. We as well as all of my family agree I can’t handle having a baby. We do both agree on adopting an older child though so we have hope for kids one day in the far future.