Have a look at Open IPC and Yi-hack (link is to one specific family of their cameras, but there are hacks available for other non-allwinmer models too).

I believe you can also hook up a raspberry pi (with a camera module) to Motion Eye wirelessly.

The easiest thing for security (though not necessarily own source) would be to find a WiFi cam that offers offline or local access and confining it to it's own subnet that doesn't have access to the internet. I think you can do this with reolinks, but double check.