Recommend a drone which is tiny and compact

Dear all,
I am looking to buy a drone which is very tiny and can be used from QGroundControl with Mavlink protocol. Due to regulation and space, I need a small one which is very light and compact to do some experiment
Hope you can guide me . The " PX4 Development Kit - X500 v2" which I bought is good and serves the purpose; however it is not easy to find a place to do some test so I am looking for a tiny ready made one.