The oral pills don't have much shown effect on uterine progesterone levels, but the suppositories do show increased local progesterone levels if done for the first 10 weeks. (I dont have the study info, but it's one my RE showed me when we were deciding on a course of action for this pregnancy.) Do you have the ability to be referred/consulted to a reproductive endocrinologist for better help with your decision? They're the ones who deal with hormone levels like this daily with IVF and fertility patients. Mine was amazing for helping me make decisions and balance hormones.
I don't have a positive story for you for not supplementing though. Kind of the opposite actually. This is the only pregnancy that's made it out of first trimester and it's the one where I finally did the vaginal progesterone suppositories and worked with a reproductive endocrinologist. My others unfortunately ended in 1st tri miscarriages likely due to not supplementing progesterone and not testing it early enough due to standard OB care having you come in for the first time around 10 weeks. (My progesterone level is around 6 without supplementing though due to PCOS, so incredibly low.)