In reply to 1234None:
Having done a bit of high-board diving in the past, I can tell you a couple of things: 1 - landing flat on your back from even 3m stings, let alone 5m, I've not been higher than that. 2 - miss-judging rotation, hitting the water still tucked and kneeing yourself in the mouth on impact gets you a week on a soup diet and a nice scar in your lip
Wearing a rash vest with a nice high neck can help take the sting out of landing on your back - I used to wear a neoprene/lycra one in high-board lessons and was quite glad of it a few times.
Surprised no-one's mentioned wearing a buoyancy aid to stop you going too deep. Apart from being a pain to climb in, it could be a blessing or a curse on the way down. If you do try one, make sure it fits - when I first met my wife, she had cracked and very bruised ribs from coasteering (works team-building thing). They'd all jumped in near the end of the trip and her BA had been a bit big (she's very slim) and the impact had forced the waist band over her ribs, crushing them.