locate on internet a weather coastal sea forcast this should include water temp if you locate a good resourse for this information what temp are you going to dive in the next part is to locate a mark make of suit that shall fit you well not tight for example salvimar to cressi are made for different builds of people look what make of suit shall benifit you they have a the mesure table in cm normaly the chest size is important ,. If you purchase a economic suit youll struggle omer i find good looking suit although the neropren is not elastic its rigid, Cressi good salvimar good for less muscular persons mares ok muscular to rebust alike cressi ,Seac new production good older model of suit fair,. The thickness of the suit depends on time of year and clear water or murky water .Winter 5c to 17 c perhaps use a 7mm suit, 18c temp to 23 c 5mm ,. 23 to27 c temp 3 mm then take into account heat temp external of water if in doubt include a under vest neropren top in cause the temp prove to be lower than anticipated