Thermo Watch will work for you if you are on a Nest account (even if you use a Gmail email to log into it). In that case, it lets you log in even after the September 1st 2019. Right now it does not support login with a new Google account. Support for Google accounts is coming soon. Note that if you are on a Nest account, migration to Google account is not mandatory.
The simplest and quickest way of controlling your Nest Thermostat*
Nest Learning Thermostat,
Together at last.
*Aside from always standing right next to it.