What company can redesign my 2012 FF seats into a Diamond Design plus provide some other tweaks .nee

I can't answer the shop part, but here's a few thoughts.

Sounds like you need a Lusso. One of the big differences between the Lusso and FF is the ride itself. The Lusso is MUCH more compliant, especially at lower speeds around town etc. You can venture into this, but there's absolutely no guarantee that it will solve your issue, and in the end it might just cost you a lot, including cost for added devaluation. You take a gamble with such a modification, because there's no guarantee that the colour will match, nor that the seats will be as comfortable as you hoped. If you think it's the Lusso seats that somehow are the fix, then I suggest you get a set of Lusso seats. I'm quite sure they will bolt right in. With those you stay OE and have a good chance of matching leather, pattern and stitching. But that being said, the Lusso and FF seats themselves aren't that different. I suspect that what you feel is the different between the Lusso and FF, because those two cars a very different in the ride comfort department due to chassis changes.