Help with DIY build!

Trying to nail my DIY hybrid build as close as possible on the first go, but have some questions before making some purchases.

If the slat spacing on my frame (KD nomad) are 2.8” wide, is it a good idea to get a piece of 1/2” or 1” thick HD foam under the coils so the coils don’t sag into the gaps between slats?

I’m thinking of getting the combo from pocket coil store with the 15.5g quad 8” and the 3” quad minis with the cover.

Would it be a bad idea to get the cover for just the coils so that way I’m not locked into any comfort layer configuration in terms of height?

Or would the cover in between layers affect the feeling of the quad mini not being directly in contact with my comfort foam of choice?

I was initially thinking of just getting the 14” cover with the combo for a bottom to top build of : 1” Lux HD foam, 8” quad coils, 3” mini quad, and 2” soft or medium latex.

After I thought it over I realized I’d be stuck with a 2” layer on top of the coil combo. Although that is what TPS recommends, I’d like the flexibility for modification, but not at the risk of changing the feel of the setup in a negative way.

Hoping someone has some insight so I can pull the trigger on some components!

@DIYMattress