A 5mm men's scuba wetsuit is ideal for water temperatures above 14°C or 58°F, remember to base your suit on the temperature at the depth you will be diving or snorkelling not just the surface temperature as this may be as much as 5°C lower. Generally for areas like the Red Sea a 5mm suit is ideal and offers the additional benefit of protection you from the sun. A simple and inexpensive way to boost the warmth of your suit is to layer by wearing a rash vest underneath or a complete body skin which has added benefit of making your wetsuit much easier to get on. Often 5mm suits will have zips at the ankle or wrist to make getting in or out of the suit easier while maintaining a snug fit, some feature super stretch neoprene so don't require zips. The choice of front or back zip is personal and all suits will normally feature a baffle behind the zip to stop water flushing into the suit and cooling it down. Remember a lot of your body temperature is lost via your head so wearing a hood will keep you warmer. Consider semi dry seals on the wrist and ankles (this is just a shiny neoprene that sits closer to your skin) that stops the warm water within your suit easily exiting when you are moving about. After each day's diving you should wash your suit in fresh water and allow to dry out of direct sunlight.