Hi p0n00w6.
Welcome to our Mattress Forum 
I think your proposed build is a solid start. Truthfully, I can’t tell you what’s going to feel too soft or firm based on your proposed build simply because what may be too soft for my liking/support needs may not be soft enough for you and yours.
I’d suggest getting your comfort layer from somewhere with a great exchange policy in the event you’d like something firmer for the 2nd layer. Essentially you have soft on soft which will definitely allow for a cradle/sinking feeling.
Your best data point is going to be putting these layers together, testing them for a number of nights, and adjusting as necessary.
I tried to look through the forum for you to see if I could find any similar/related threads that may be useful to you. Perhaps this conversation and this one might have insights you find helpful.
NikkiTMU