2005 Rear shock

Hey guy's
A mate has a 2005 ZZR600 and feels that the back end on it is way too soft for his liking.
We were out a ride the other day and it bottom out and i think he nearly shit himself so he's on the hunt for something that will make it a little stiffer and give him a bit more confidence.
He's checked the price of both a rebuild and uprated shock and had to change is undies again lol so what options does he have???
I've heard that he could use the ZX10 rear shock from an 05 bike but i've also read that he could use a 636 shock as well.
He's not too technical so would prefer something that is a straight fit.
All help is appreciated as always.
A mate has a 2005 ZZR600 and feels that the back end on it is way too soft for his liking.
We were out a ride the other day and it bottom out and i think he nearly shit himself so he's on the hunt for something that will make it a little stiffer and give him a bit more confidence.
He's checked the price of both a rebuild and uprated shock and had to change is undies again lol so what options does he have???
I've heard that he could use the ZX10 rear shock from an 05 bike but i've also read that he could use a 636 shock as well.
He's not too technical so would prefer something that is a straight fit.
All help is appreciated as always.