Please update. I appear to have the same setup as you and would like
something smarter without overdoing it.

In particular how easy or otherwise to remove the timer mechanism.

Our boiler is in a back utility room extensions so the wireless signal
as a way to go as well.

I can only speak for the Hive system but should imagine other smart systems are pretty much the same. The basic system consists of the wireless thermostat that communicates with a receiver that is wired to the boiler and a hub connected with CAT5 to the router and communicates wirelessly to the receiver. If you do not intend to use the app to control the system or over the internet then the hub is not required. The receiver only needs to be placed where it will receive a signal from the thermostat and likewise the hub but needs wiring back to the boiler.

In our instance the router is in the hallway and so is the hub and the receiver, the receiver is wired through the wall to the boiler which is situated in an airing cupboard in a bathroom off the hallway. As for the thermostat that can be fixed permanently to a wall or mounted on a stand and taken to different rooms. I have tried it in various locations and it has not failed to communicate despite all internal walls being of block construction.

Richard