As Graham suggests, it looks like Insteon have a product that will work (although maybe not an ideal fit). This is a mains-powered unit that implements low voltage switching and sensing. In order to interface to Alexa, you'd need the Instron hub too.
As an alternative, you could use 433 MHz modules and implement our own hub using a low-cost SBC (this may not save much in the long run, but could be an interesting project if you're so inclined). It is true that the majority of 433 MHz modules are one-way, mainly because of problems with battery drain at the remote end.