Preventing pregnancy with ovulation test?

So my boyfriend has never finished inside of me before not even with a condom and we really want to try having him finish in me just once. I’m on the mini pill (norethindrone), but I’m too scared to have that be the only form of protection we use. So he said I could take a plan b, but I know it doesn’t work if you’re already ovulating and with the mini pill you can still ovulate. So if I’m very careful to take my pill right on time everyday, then I take an ovulation test to see if I’m not ovulating, he finishes in me and I take a plan b, then it should be good enough to ensure I don’t get pregnant right? Again this is only so we can just see one time how it feels to have him cum in me.