Welcome to the Classic Cougar Community. I sent you a welcome email it contains a lot of information for the Cougar owner. If you do a search on this site or Mercury Cougar.net you should be able to find a seat combination that will work for your needs. I have seen many types used as stated above by OldWood even Porsche seats have been used. Jody has used Jaguar seats in his convertible conversion.
Here is a link to his CopyCatVert thread.
I hope this helps.
Steven