Even if water is warm, a "skin" would be suggested in case you come into contact with something that may irritate your skin...and naturally, we are all different and you should just be prepared so that you are comfortable, some people do ok with full wetsuits like 3mm’s, some like shorties, some like other combos, you need to find your thresholds...some people can handle cooler water better than others, but remember that your always losing body temp diving, especially for longer dives. And we haven’t even addressed those thermoclimes that we occasionally run through.