Please Help Choosing Latex ILD for Hybrid Mattress

After a TON of research, I am planning on constructing my own hybrid mattress with combi-zoned pocketed coils made by Legett and Platt with a 2" or 3" (probably 3") latex comfort layer on top. I am 5’8" and about 150 lbs and my partner is just a tad heavier, curvy, and a tad shorter. I am a strict back sleeper and my partner is a strict stomach sleeper. We like our mattress to be pretty firm. I almost pulled the trigger on an Avocado mattress because I know I would like the feel of that mattress, if that helps maybe give an idea what I am looking for (7-8 out of 10 on the firmness scale). I obviously do not want to sleep on a rock though either. If I were to get 3" of latex, what range of ILD would be good for my situation? I will most likely get dunlop as the comfort layer, but ILD suggestions for both talalay and dunlop would be greatly appreciated.