Thank you Victor & Mike fro answering. I think I didn't explain well the needs, sorry for that.
The sensor should be small, less than 4 mm diameter, similar to this: http://www.electronics123.com/new-products/MuC213-Camera-Module.html
Such sensor should be connected by wire, 1 meter long, to a small transmitter.
The transmitting range can be short, within a room, so no need for strong transmitters like you suggested.
All should be battery operated, and easily handled and carried.
As for Video resolution, I didn't assess it yet.
Of course, better quality is preferred, but only if it is not conflicting with the size.