What suit type are you using?

I am thin but have an ocean dry Bravo which is neoprene so insulates unlike the thin ones.

I wear a pair of thin fleece pants and tuck them into my socks with a good old green short sleeve swazi fleece top when it's winter.

A good hood and gloves do a lot to help.

Summer I wear shorts and a tee shirt.

I ditched my bcd a few years ago and that feels pretty good in terms of streamlining what is a bulky way to dive.

I wouldn't go to deep without a bcd though.

I am way north and I suspect in warmer water as well!