It may not be the clutch. It could possibly be the clutch cable. They are wonderful about gumming up and fraying!
Now if you are looking for a good clutch to an otherwise stock powered car, anything the local parts house offers is just fine. I dought you are gonna find an easier on the leg operating clutch over a low buck clutch. Id say start by checking out the clutch cable and possibly clutch quadrant too.
I would have to agree that the stock clutch was harder to push than my 4 cylinder ranger but I never had a problem kicking the clutch when I was 18. As blak said replace the cable, give the quadrant a good inspection and see what that buys you.
First off, welcome! Post up some pictures of your Mustang!
Piggybacking on what the other two members have said, start with checking the clutch quadrant (located under the dash) a good inspection. If you decide to replace the clutch cable i highly recommend getting either a Ford, Steeda or Maximum motorsports cable. Almost all of the other cables are not made to the same standard and often snap, leaving you without a clutch and making a drive home much more difficult.
If the clutch still hasn't improved, then consider replacing the clutch with anything the local parts store has or even something off of RockAuto.