Get an AW watch, then. Unless something changed since I sold my Gear S in December, there is no Tizen whatsap app support. There is an app called Gear Notifications or something similar that was a work-around to this, but on my current watch, I can read and answer whatsap messages and calls. My watch was taken off the market, but may get re-released soon: the LG Watch Urbane 2 LTE. It comes unlocked and works overseas, so if you travel a lot, you could have a sim card of whatever country you are in inside, and keep your US sim in your phone.All I need is discreet notifications and ideally the ability to respond to messages, since I'm going to an Android Phone I will likely be using WhatsApp since me and my wife are often in different countries so we need a messaging option that uses data rather than sms.
This all goes way beyond your expectations from a smartwatch as listed above, but it's some food for thought. I would NEVER go back to Tizen. Since you have a 360 now, you may just want to wait a little for whatever comes to market soon. The Sony SW4 is also rumored to include LTE.
ETA: BTW, I also have Google Hangouts and Skype on my watch, great additions to Whatsap, and they also were not available on my Gear S/Tizen.