I ran an FIA approved harness in my old RX7. I've use Simpson, Sabelt, etc. I did not like my Sinmpon, mostly because of the latch. PITA. I did like my Sabelt, it was a camlock. Make certain you get a real harness (3", certified, etc). I suggest getting a camlock.

Personally, in your case, I would just get my sealtbelt fixed. Isn't there a law that the manufacturer has to replace it if it breaks? You should double-check that.