Unless I’m missing something, I think @Karosm’s suggestion to use a Shelly 1 is solid.
It’s a single component which can handle 240v and detect the doorbell being pressed.
No need for parallel circuits and requires less rewiring than what you currently have in your diagram. The best thing is, it will not interfere with the original bell functionality except in the case of a hardware failure.
Diagram below, just imagine the lamp as your bell
