Just looked at your original posts you say you were freezing in 85F water - 30° I dive that water temperature maybe down to 28°C (82 F)in 0.5mm frogskins. and many people I dive with in those waters are in shorties or boardshorts. _ goes to show that people vary widely in their cold tolerance and taking people's advice on what exposure protection to use should be taken with a good sized grain of salt.
When you say 4/3mm suit I assume you mean 4mm body/3mm arms/legs? Certainly a suit that fits well will help a lot - less exchange of water - but things like leg/wrist/neck seals - dry zippers etc are probably equally important. You may want to look at 5/3mm suits or as you seem to feel the cold a full 5mm suit??