I lived in Shanghai for a while and were put on to these guys:
Slumbermaxx
We now have one of the executive foam mattresses and wouldn't have anything else - no issues with overheating, comfortable, soft but firm where it needs to be. We have bought very expensive mattresses before in the UK and nothing we've had comes close to this.
Plus, they give you a 15 night money back guarantee so you can give it a try. All you pay is the (pretty small) shipping cost if you return it. They do ship to Hong Kong even though it's not listed on the website.