any Spring recomedations?

I have FRPP B springs in my car and it rides closer to stock than most other springs I've tried. I don't think it will sit as low as your Steedas though. Maybe check out Bullitt springs also. They're a bit lower than Machs if that's a concern. Not much else comes to mind. I know this isn't what you're looking for, but I've put 15" Prostars and Telstars on some of my old cars and it rode a lot smoother because of all the extra sidewall with the 15" tires. I put 4 cylinder fox body springs in the front of one of them also and they rode quite soft.

I had Eibach Pro springs, they are 1.5" drop, look pretty good (not low enough for me but I like cars slammed) and it rode pretty darn soft for a lowered car.

Tough call. Lowering requires hugely stiffer spring rates, which is not what you want.
A progressive spring will help.
Also it sounds like you might have damper issues (harshness often involves a lacklaster set of struts/shocks).

Seats are not too expensive when considering swapping springs and dampers. Make a suspension for your seat? (I have bad back problems myself).

Good luck.