Quote, "the sag only sets up how good the suspension works not the comfort".
Yes, that's my point, why do you think it's the suspension that's causing you the trouble? Unless it's bottoming out, which I doubt.
I would be looking at the seat comfort & ways to make it better. There's plenty of posts on here about using 3D seat covers, sheepskins etc. all at sensible money, then, if they don't work well enough you can spend your hard earned on a remodelled seat, different foam or gel insert?
You say you've used an Airhawk, have you got too much air in it? They work best almost flat!