We replaced our 20-year-old Beautyrest (World Class Norcross Plush Eurotop) with a Naturepedic EOS Classic Plush (Plush 8" encased coils with edge support, soft 3" latex on top). I really don’t like the feel; it is too bouncy/latex-y for me, I need something that gives a bit more since I am a 150 lb, 5’10" side sleeper. I sleep hot and the latex was making my back hurt because it was too firm for me. My husband is fine with his side (plush coils, medium latex), so I am just going to change my side. I figured I will keep the coils and the cover since they’re good quality and I love innerspring mattresses. I tried swapping out the soft latex for a layer of soft microcoils, but I feel like I still need something more cushiony, similar to whatever they used to use in old Beautyrest innerspring mattresses. What should I put in that top 3-4" layer above the coils that will make it feel like my old Beautyrest? I got a recommendation for the Foam Factory website, but there are so many different types of foams on there, how do I know what density, type, and thickness I need? Any recommendations for recreating an older innerspring mattress, the kind that had a plush top? Should I do 1" of some sort of latex, 1" memory foam, 1" polyfoam? Will that give me some support but help with pressure points and keep me cool? Would love suggestions for specs if anyone has them. Thank you, I am so overwhelmed!
Hi The650life.
Welcome to our Mattress Forum. 
It sounds like quite the adventure, DIYing your half! I believe the Beautyrest used polyfoam and tufted the mattress (in other words, it wasn’t a foam slab over innerspring coils, it was a thick layer of batting, essentially).
We sort of shy away from trying to match feel of a specific mattress because, honestly, it can be nearly impossible to do. You can have identical mattresses and if you change something small like the encasement or the stability layer, you ultimately change the feel of the mattress. Instead, we recommend focusing on adjusting your mattress (or in this case, your side of the mattress) to the correct comfort and support for your needs.
What did they recommend for you? I’d be super interested to know!
We can help with density! We have guidelines for that 
Thickness sounds like it’s determined by the existing foam which you’ve said is 3" - unless you’re okay with having a taller side than your partner. You could theoretically have more comfort layer material if you need it (but also have to take the encasement into consideration). Type is also totally subjective and based on what you like.
I would suggest looking into a shredded latex topper or wool topper/pad to help create some of that plush pillowy feel atop 2" of a foam (latex, memory, etc. whatever you prefer), maybe a medium-soft latex that you can sink into.
That’s my top-of-mind idea, but I’m sure there are a few people in the forum with ideas to share as well! Please let me know what questions arise.
NikkiTMU
Oh when I said I got a recommendation for the Foam Factory, I meant somebody told me to try there for foam, but I don’t have specific recommendations for type of foam, which is what I am trying to find! Density, thickness, type, etc. There are so many I don’t know where to start.
@NikkiTMU thanks so much for your help! I clicked on your link to guidelines for density, but it just took me to the home page. What density would you think I should get for a 2" layer of polyfoam and a 2" layer of medium foam to put on top of the innerspring coils if I wanted a medium-firm but plush/cushiony feel?