The most common wetsuit complaint is being cold in one, and the most common cause is a suit that is slightly too big. It is worth understanding why before you spend money.
How a wetsuit actually works
Not by keeping water out. A thin film of water enters, your body warms it, and the neoprene stops it leaving. A loose suit lets that warmed layer flush out and replaces it with cold water every time you move - which is why a baggy 5 mm can be colder than a snug 3 mm.
The four places fit matters
Neck, wrists, ankles and the small of your back. A gap at the lower back is the classic flushing point and the hardest to notice in a shop while standing still.
Getting one on should be difficult
A dry suit that goes on easily is too big. Two minutes of undignified struggle is correct; pain, restricted breathing or not being able to reach your own tank valve is not.
For the Andamans
The water sits between 27 and 31 degrees. A 3 mm shorty is right for most people and a rash guard is enough by March. Bring a 3 mm full suit only if you feel the cold or you are doing four dives a day.