I've found model TZ43 that is 5”x3”x3/4” from Residential Control Systems Inc, and ordered one online for $175 US. If it does not fit or I don't like the look I'll try a 2-piece unit instead.
As for looks, the Honeywell WiFi Smart Thermostat RTH9580WF looks perfect from a size and form factor, but I don't see API info on their WiFi protocol to see if it would have the same issues as the nest.
Edit: In case anyone comes across this thread. The Manufacturer web site said 5x3x3/4, but the specs in the product sheet are 6x4x3/4, and actual size is 5-3/4 x 3-15/16 x 1/2. I contacted RCS to ask them to correct it. It does overlap, but it does not look bad. I' gonna keep it.