I'm sorry but Catholic or not after 4 kids and with no desire to have more I would use any.contraception.I could, regardless of my beliefs.
Nfp works great we use it to get pregnant and to avoid. So far 14 years no slip UPS. However you have to stay on top of it not have *** or you will get pregnant. I use a website to chart doing it by hand is to much.work and leaves room for error.
Implanon is still considered birth control. I was raised catholic and I know they don't like it but you may just have to. You can try timing your periods so you know when you are ovulating and avoid sex. I'm not sure if they class the withdrawal method as birth control but that's not really 100% either..
You can look into natural family planning. My husband doesn't want any more and I don't like the idea of birth control. I'm Catholic too so I'm feeling guilty bc my husband is using condoms. I am thinking of researching NFP.
U should get the implanon...3 years in. No need to worry about any other contrception