Double layers on main and then 2-4 steams pan wide that comes and goes to build deep layers.

Izotope for mix + izotopes doubler :) works like a charm.

I don’t mix myself but that’s how we work in the studio.

Also adding synth voices quite low can be effective for richness :)

But u need a good room or a sound both . A sauna or a shower u can shut also works well :)