Videomaker – Learn video production and editing, camera reviews › Forums › Cameras and Camcorders › Consumer Camcorders › Looking for best Urbex camcorder/camera – $500-$1200 › I am afraid for your filming
I am afraid for your filming style there will barely be anything much better. And any camera, even the low light monster like A7s (useable only with manual focus, BTW), still needs light or you are looking at infrared.
With any bigger sensor cameras depth of field will be thinner, so accurate focusing is a must. I hear that Sony A6300/6500 AF is quite good, both are decent low-light performers, and the latter got IBIS which will be very useful for your handheld operation.