I don't get cold easily, but I absolutely hate being cold.
In warm waters (like the Caribbean, for example) swimsuit and rash guard.
If it's just a bit too cool, I go with my 1mm open cell freedive suit - it has the warmth of approx 3-4mm without buoyancy issues.
That suit covers most water temperatures for me until it gets down to 'cool', at which point I switch to either my 7mm semi-dry (no hood) or my 7mm hooded topper - my legs are the last part of me to get cold.
If it gets cold, I pair the 7mm semi-dry with the 7mm topper (which has a hood), 5mm boots, and sometimes 3-5mm gloves (I hate wearing gloves and if I do have any, it's usually just a lightweight pair of reef gloves).
Anything below 50F or so, I add the freedive suit under the semi-dry and topper and then I'm almost too warm.
For surface intervals, particularly if it is cold, I pull down my suit and let out as much water as possible before climbing into my boat coat (I have a huge Surf-Fur and I love it). The freedive suit adds a lot of warmth, it just requires lubing up to get into it. Before splashing for dive 2 (or 3, or 4) I usually fill the suits up with water as warm as I can stand so my body doesn't have to work so hard to heat up a new water layer once I'm in.
In the future I may get a 3mm or 5mm freedive suit to further cut down the buoyancy while keeping the warmth - of course, that won't help on very deep dives (which is why I have the semi-dry).