Hooking a wifi thermostat to a 2 wire boiler

I’m in the process of figuring out how to swap my existing thermostat for a new WiFi thermostat. Naturally it’s connected to my home’s boiler by 2 really old cloth wrapped wires. Examening the wires, it does look like I it should be feasible to run a new wire which also hooks into the C screw on my boilers transformer, but I’m the sort who likes to act cautiously on this sort of thing of course, so I was hoping someone could give me a quick yes/no on my reasoning, as well as see if there’s anything I missed.

Anyways, on the technical side, the furnace I’m hooking the thermostat too is a Weil-McLain boiler (Link https://www.weil-mclain.com/products/eg-gas-boiler), and the transformer in it I’m looking to tie into is this one here: (http://www.supplyhouse.com/Weil-Mclain-510-312-166-Transformer-120-24V). There’s curently a wire running off the C connection on the transformer, it looks like to the water fill unit, does that raise any concerns?
Anyways, thanks for any advice.