Sonoff wired at celling rose UK
Sonoff make several different products, if this is their "BASIC WiFi Wireless Smart Switch" it has N,L in and N,L out. It presumably connects L in to L out on receipt of a signal from a remote control.

You show the switches wired in parallel, which should work as you describe:

s1  s2  lamp
--- --- ----
on  on  on
on  off on
off on  on
off off off


It is doubtful the device is designed for use inside a ceiling rose. It may be hard to find space there. The device might be unable to dissipate heat in a confined space. Ideally you'd ask the manufacturer for advice.