Sounds like we have pretty similar hair! My waviness has greatly increased in the last few years since I've been co-washing, so definitely stick with that for a while.
My hair, if left to dry natural dries in a big swoopy yucky wave. What I have been doing for probably 10 years now is after I scrunch, I put in a big ol' jaw clip before I let go to secure the scrunch into place while I finish getting ready for the day and even while I dry my hair with a diffuser. There have been times when I've left my "Secured Scrunch" in too long and ended up with wayward kinks but have learned not to let it get too dry before removing them for the last few minutes. This REALLY helps the curls form to begin with and helps them stay since, at least for my thick hair, its own weight tends to pull the curls/waves out.
I put a leave-in & gel into my wet hair. scrunch some water out. scrunch with a t-shirt. scrunch with hand to secure with a few big jaw clips around my head. 3-4 usually does the trick.
Try it! ...especially since you say plopping seems to help; i think this is better! (but then, since I didnt know about plopping when I experimented with this, why wouldn't I?